Depends on your definition. If by "community", you mean an organized group or society, as the original Latin term communitas, then certainly it is possible. Atheist Nexus; Atheist Alliance International and American Atheists are three examples of such "communities".
If "community" brings to mind images of shared resources; common values and cultural elements; and social cohesion, then the question may be a bit trickier to answer. There is no question that many who self-identify as atheists have these sorts of relationships and interactions with one another.
The question is: are these interactions the result of shared "atheism" (defined as a lack of belief in a god or gods) or are they the result of shared positive beliefs that often accompany atheism (humanism; anti-theism; a commitment to reason, science, human rights, etc.)? Can a negative provide the impetus around which to form relationships? Or do they form as a result of the positive, shared ideas?
The idea has important implications for those wishing to forge closer ties between nontheists-rather than seeking to model an atheist community after an ethnic or religious group, with a core identity and belief set, it may be more practical (and effective) to conceive of a loose-knit coalition of communities built around key causes, values and ideas with strong interconnectedness.
These would be similar to a person's national identity in a modern pluralistic country where an individual's multiple roles and identities are infused by the concept of national identity, but not subject to it. The Internet itself also provides a useful model with high degrees of interconnectedness throughout the network while maintaining national and specialized networks within the overall structure. These networks meet specific needs while also serving as the Internet.
Thus nontheists can nurture community around science, justice, shared interests and any number of other elements while holding to a greater atheist identity. Greater, yet also more abstract with fewer shared cultural or intellectual elements. With this model, communities can develop and flourish with unique characteristics and trait, but the entire atheist population can benefit from the results.