I was recently asked this question, which is apparently still a live one. There are Christians out there who believe that other Christians can be demon possessed or “demonized.” I must first begin with the humble admittance that I am no expert when it comes to personal experience with demon possessed people. I have never participated in a real exorcism that I am aware of. All I can say is based on what I know from Scripture.
Two issues complicate the question. The first has to do with identity—what makes a person “Christian”? “Christian” is mostly an anachronistic term for the followers of Christ in the New Testament. It does not become the universal norm for identifying all of Christ’s followers until many decades later. In the New Testament we find the term only three times. It identifies the congregation in Antioch (Acts 11:26). Herod Agrippa II also poses the response to Paul that in a short time he wants to make Agrippa a Christian (Acts 26:28). Likewise, the Petrine author uses it in relation to suffering when writing to churches in northern Asia Minor (1 Pet 4:16). That’s it. I suggest “Christ-follower” as the more appropriate NT term. A Christ-follower is someone who trusts in Jesus as Messiah and the risen Lord.
The second complication has to do with our determining what demon “possession” and being “demonized” means. At least in reference to the latter, some suggest that this is not the same thing as possession but can be something like being oppressed or harassed by demons. I have no problem accepting that such phenomena can happen to Christians. For example, Paul’s “thorn in the flesh” came by way of a messenger of Satan buffeting him (2 Cor 12:7). But that is different than demon possession. 
Demon “Possession”
A biblical understanding of demon “possession” seems to suggest that a demon “dwells” in the body of a human. The body is sort of like the host for a demon (or demons), who presumably influences the person. It also may be the case that the mind and volition of the person are either influenced or overridden by a demon. In such cases in the Gospels and Acts, demons are cast “out” of the person by the authority of Jesus or his apostles.
The man who was naked, cutting himself with stones and living among the tombs in Mark 5:1–20 (and Gospel parallels) comes to mind. Jesus commands the demonic presence to “come out” (ἔξελθε < ἐξέρχομαι/ exerchomai) of the man. The term “unclean spirit” describes the demons, and being demon-possessed or “demonized” (δαιμονιζομένῳ/daimonizomai ) describe his state. In that case the man was a gentile, originally a non-believer.
Even so, “unclean spirits” may be present in apparently religious people, too, as was the case with a certain man in the synagogue (Mark 1:21–28). Again, Jesus commands the spirit to “come out” of the man.
There is no biblical evidence directly supporting phenomena like this in which the demon enters or dwells in a Christ-follower so as to necessitate being cast out.
There are only three examples I’m aware of in which potentially a follower of Christ might be considered demon-possessed: Judas, Ananias, and Peter. Each of these cases are unique.
Judas Iscariot and Demon Possession
Satan is said to have “entered” into (εἰσῆλθεν < εἰσέρχομαι) Judas Iscariot when he was betraying Jesus (Luke 22:3; John 13:27). Problematic here is that Judas is possessed not by any standard demon or unclean spirit, but by Satan himself. Another complication is that we do not find Satan talking through Judas or otherwise hijacking Judas’s mind or will. Even so, Judas is purported to be a Christ-follower, and an evil spirit (Satan) possesses him in the sense of entering into him and doubtless influencing him.
But is Judas an authentic believer? John’s Gospel has Christ discerning Judas’s duplicity much earlier than the betrayal (John 6:70–71). But this does not necessitate that Judas never was authentic, at least in comparison with the other Gospels. Judas, for example, seemed to be empowered by the Lord to cast out demons as one of the Twelve disciples (Luke 9:1). Hence, in Luke’s Gospel at least, Judas is every bit a disciple as the others. In fact, Judas as one of the Twelve, will reign in God’s future kingdom; he will sit on one of the thrones and judge the twelve tribes of Israel (Luke 22:38–30; Matt 19:28).
After his fall, however, he needs to be replaced by another apostle (Matthias). The assumption is that Judas will not enter the kingdom of God; there is a vacant position on one of the twelve thrones (Acts 1:15–26).[1]
A new question to ask, then, is whether Judas was at one time an authentic believer but fell away, and that is when Satan “entered” him. If so, then we do have something similar to an example of a backslidden or apostate Christ-follower being “demon possessed.”
Ananias and Sapphira: Satan filled Ananias’s Heart
What about Ananias, husband of Sapphira? It is said that Satan filled his heart to lie to the Holy Spirit (Acts 5:3–5), and we can contrast these words with being filled with the Spirit, which happens frequently in Acts. But once again, we must question whether Ananias is an authentic or inauthentic Christ-follower.
Even if we assume Ananias were a true Christ-follower, there is still a question about whether or not he was actually demon (or Satan) possessed. In Acts 5:4 the Greek word tithȇmi (ἔθου as an aorist middle) seems to explain what this particular “being filled” means. It means to contrive or ponder something in the mind or heart (cf. Luke 1:66; 21:14; Acts 19:21). Satan may have influenced Ananias, but there is no clear evidence that Satan actually possessed him.
Had Satan actually possessed Ananias, we might expect Luke, the purported author of Acts, to use language similar to Luke 22:3: “Satan entered into Judas” (εἰσῆλθεν … σατανᾶς εἰς Ἰούδαν). The meaning instead seems to be that Satan influenced the thoughts, plans, or motives of Ananias (cf. Luke 5:22; 9:47; 24:38).
Peter Rebuked: “Get behind me, Satan!”
What about Peter? He was rebuked by Jesus who said to him, “Get you behind me, Satan!” (Matt 16:23). Peter was attempting to get Jesus to evade his upcoming death. Jesus thus responds to Peter not because Peter was demon possessed, but Peter, like Satan, was thinking in a way contrary to the way God. Had Matthew considered this to be demon possession, we might expect him to speak of this incident in terms of Jesus “casting out” Satan from him (Matt 10:1; 12:43), and Peter being demonized (δαιμονίζομαι: Matt 8:16, 28, 33, etc.).
Conclusion
Nowhere in the New Testament do we find a clear-cut case of an authentic Christ-follower that is demon-possessed. However, we do find the possibility that a person who used to be a Christ-follower can be possessed by an evil spirit—Judas. Likewise, Ananias was egregiously influenced by Satan.
Application Today 
If Christians are baptized into the body of Christ and have the Holy Spirit living in them, it seems contradictory to say that those who faithfully abide “in Christ” can be demon possessed (Rom 8:9-11; 1 Cor 12:13; 6:19; 1:30; John 15:1-5; compare Matt 7:16-20; James 3:11-12). Christ has delivered Christians from the kingdom of darkness, and the devil cannot harm them in any ultimate sense (Col 1:13; 1 John 4:4; 5:18). I do not believe that Spirit-filled Christians can be demon possessed.[2]
On the other hand, as the example of Judas shows, there is always the possibility that backslidden Christians can be demon possessed or demonically influenced. In Scripture we also find that those who have committed apostasy or committed heinous sins are sometimes “delivered over to Satan” (1 Cor 5:5; 1 Tim 1:20; compare 1 John 5:16-18).
I also realize that a number of Christians honestly struggle with various types of sins, whether sexual vices, drugs, pornography, stealing, etc. Often the problem is our own sinful nature, not necessarily demons (James 1:13-16; Gal 5:19-21). The Bible never commands Christians to have demons cast out of them whenever they sin. Instead, they are to confess their sins and turn away from them (1 John 1:9–2:6).
Whether or not demon oppression or strongholds are part of the problem, these individuals should seek to find freedom through repentance, prayer, having other faithful believers pray for them, and abandoning whatever entices them to return to the same vice. Also they should regularly attend a mature church, develop a strong devotional life, and join an accountability group. Sometimes professional counseling also may be needed.
Notes
[1] See further B. J. Oropeza, In the Footsteps of Judas and Other Defectors: The Gospels, Acts, and Johannine Writings (Cascade).
[2] See further my 99 Answers to Questions about Angels, Demons, and Spiritual Warfare.
Image 1: Explosion Army Soldier Military War Attack via pixabay.com; Image 2: Feel Free Silhouette Joy Achievement Arm Boss via pixabay.com
Ad-Free & Subscriber Log-In