The simple answer to this question is "Yes". Now, the things is that we are made in the image and likeness of God. God is a three part being (Father, Son and Holy Spirit). Humans are also a 3 part being having a body, soul and spirit. When a person becomes a born again believer, the Holy Spirit comes in and dwells in their spirit and no unclean thing can enter there. As for the body and soul, it's a different situation. Demons CAN dwell in them. Many physical and mental issues are caused by demonic OPPRESSION, not POSSESSION. They are 2 different things. A non-believer can be possessed by demons though because they do not have the Holy Spirit living in them to stop the possession. There are many ways a person can get demons. Sin is the main way. Anytime a person sins, they open up a door that a demon can enter. That is why it is so important to repent as soon as you realize you have sinned so that the door can be closed. People can also aquire demons at conception such as being conceived out of wedlock, generational curses and parents being involved in occult practices just to name a few. Fortunately, we have an awesome God who allows us to take authority of these demons in Jesus name and cast them out. All believers have the ability to cast out demons.