You could be considered a pagan if you don't believe in religion or you worship more than one god.
The original pagans were followers of an ancient religion that worshiped several gods (polytheistic). Today, pagan is used to describe someone who doesn't go to synagogue, church, or mosque. It could be that they worship several gods at once, or they have no interest in a god at all. Religious people sometimes use pagan as a put-down to describe the unreligious as godless and uncivilized.