You can call him/her, Non-Christian.
If you are asking what you call someone that doesn't believe in God, then that's an atheist.
He or she is an Agnostic.
An atheist; or hey you.
an atheist is a person that does not believe in religeon whatsoever
an atheist is someone who doesn't believe in a god.
If you only believe in one deity, you are monotheistic.