While atheists lack a belief in God, everyone including atheists have the burden of proof or evidence as both atheism and theism are beliefs.
One believes there is a God and the other believes there is no God. Both are beliefs. Too often atheists hide behind the idea that their lack of belief in God means they do not have a belief when clearly they do. In this video, a good argument along these lines is made when Frank Turek converses with an Atheist during question time in a presentation at California State University. The atheist storm out part way through Frank’s explanation after refusing to give an argument for his world view.