If do don't believe in any god, then you are an atheist (in the sense of, "not a theist"). For more details on that and another meaning of "atheist," see:
http://atheistforums.org/thread-32548.html
http://atheistforums.org/thread-32548.html
"A wise man ... proportions his belief to the evidence."
— David Hume, An Enquiry Concerning Human Understanding, Section X, Part I.