Short answer is yes. One can be a Christian and not believe everything God has said in the Bible. I'm assuming that is what you really referring to. Who among us is firmly set in our hearts and minds about everything God has said while we still contend with the natural as well as the spiritual man and in a constant state of growing in knowledge and grace?
It occurs to me that is what the Lord was getting at when He said, 'And he saith unto them, Why are ye fearful, O ye of little faith? Then he arose , and rebuked the winds and the sea; and there was a great calm.'
Interesting that John never mentioned this criteria for identifying a Christan brother. Now anyone can claim to be a Christian but does the one have any of the hallmarks that John mentions in his 1st epistle I think is more to the point.
If we say that we have fellowship with him, and walk in darkness, we lie , and do not the truth:
If we say that we have not sinned , we make him a liar, and his word is not in us.
He that saith , I know him, and keepeth not his commandments, is a liar, and the truth is not in him.
Who is a liar but he that denieth that Jesus is the Christ? He is antichrist, that denieth the Father and the Son.
If ye know that he is righteous, ye know that every one that doeth righteousness is born of him.
Whosoever hateth his brother is a murderer: and ye know that no murderer hath eternal life abiding in him.
Paul's statement in Romans is poignant as well, But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you. Now if any man have not the Spirit of Christ, he is none of his.