Belief -
http://www.merriam-webster.com/dictionary/belief
1: a state or habit of mind in which trust or confidence is placed in some person or thing
2
: something believed; especially : a tenet or body of tenets held by a group
3
: conviction of the truth of some statement or the reality of some being or phenomenon especially when based on examination of evidence
If you want to say atheists have belief in the third definition of the word - ok.
But the first two definitions are the ones that are related to religious belief.