@selzero no, agnosticism is the claim that it's impossible to know, regardless of existence.
This can be a basis for strong atheism («it's impossible to know, therefore it doesn't exist», which is basically Russell's teapot argument), but is also compatible with weak atheism («it's impossible to know, and/so I don't have a particular opinion about its existence»), but also with theism («it's impossible to know, but I still believe it exists», which is actually the basis of pure faith).