Yes. there's this hair's difference and maybe a difference in attitude.
As I see it simple Atheism is merely the lack of a belief in God or gods. It's not a belief. It makes no positive assertion.
However Atheism can also be a statement of theology, that is "God does not exist." And as such is a statement of belief, "I believe God does not exist."
One may not say it directly in those words, but by making it a view to be advocated, it can easily become such a theological belief.
The person who believes god does not exist may go out of hir way to disallow any position that might serve god belief. For example, since "consciousness" is seen by some as some kind of divine property, ze might simply advocate the position that "consciousness" doesn't really exist (The P-Zombie).
The person who believes God does not exist will have little tolerance for agnostics, and call that a coward's position.
But I'm sure that a good number reading this will reply that they don't believe that God doesn't exist. They know God doesn't exist.
I can't say that for myself. Having no basis to know God exists, I simply neither have that belief or that knowledge that God doesn't.