Depends on what your definition is. As how I and from my experience, most atheists define atheism, atheism is the lack of belief in god for whatever reason. Your reasoning for this can stem from gnosis (knowledge) or agnosticism (without knowledge).

Most atheists are agnostic atheists, who do not make any claims regarding the knowledge of existence of any particular gods.

Gnosticism/Agnosticism is a separate concept from theism/atheism and can be applied to other concepts, not just gods.