Usually, theists, and some irrational atheists too, go on to claim that atheism is also a form of belief, just like theism. Now, by definition, it is exactly the opposite: a disbelief. However, it can be considered a belief if you go by the strictest of definitions, but it is still not the same as theism.
Just to make it simple, replace god with any other fictional creature such as a unicorn, or a dragon, and then ask yourself the same question. You will realise how absurd that notion is.