Yes, I believe a person can be possessed by demons.This happens when the person allows evil, bad thoughts(demons) control him or her.
to keep demons out it is good to do this
Philippians 4:8 Finally, brethren, whatsoever things are true, whatsoever things are honest, whatsoever things are just, whatsoever things are pure, whatsoever things are lovely, whatsoever things are of good report; if there be any virtue, and if there be any praise, think on these things.
But also if we follow Yahshua's commandements or instructions(which are Yahwe's instructions) out of selfless love and not to avoid punishment, then we are also blessed with the Holy Spirit (Yahweh's righteous mentality) or as the last verses say, ''Yahshua and Yahweh will come and make their abode in us leaving no place for demons.
John 14:15-17 15If ye love me, keep my commandments.
16And I will pray the Father, and He shall give you another Comforter, that He may abide with you forever;
17Even the (YHVH's) Spirit of Truth; whom the world cannot receive, because it seeth Him not, neither knoweth Him: but ye know Him; for He (YHVH) dwelleth with you, and shall be in you.
John 14:22-23
22Judas saith unto him, not Iscariot, Lord, how is it that thou wilt manifest thyself unto us, and not unto the world?
23Yahshua answered and said unto him, If a man love me, he will keep my words: and my Father will love him, and we will come unto him, and make our abode with him.
Blessings,
YahismySavior