cybersex is a forum of mutual masturbation, so depending where you draw your lines as to what is "cheating" then thats where the lines are drawn for cybersex. To me, it is cheating. To some people it wouldnt be.

To some people blowjobs aren't cheating either, but i'm not one of those.

Cheating is about where boundaries are and weather those boundaries get crossed. If you've made it clear to each other that its okay to have cyber then no its not cheating. If you haven't talked about it, I would avoid it as I'd lay good odds on most people considering it to be a form of cheating.