Because everyone has a different interpretation of what cyber is, you won't get an answer that is tidy and concrete.

I am on the fence with this question, I do think that yes it is cheating, but I also agree with Oz, watching porn, reading porn, or even going to see strippers is the same as cyber, and it is not cheating.

It all comes down to how your relationship works, and how each individual feels about it. It also depends on what your interpretation of cyber is.
I get the idea that not everyone has the same definition of what cyber is either