Depends. It could be addiction, or it could be dedication. Perhaps even curiosity, commitment, or exhaustion. (There are times when I'm so worn at the computer that I sit and stare for long periods of time, accomplishing nothing but sitting and staring.
In my case, I often spend as much as eight hours at a stretch in front of my computer on HubPages, but I'm defintely NOT addicted. I have a job to do, I enjoy the work, but I don't miss the screen or the keyboard when I'm away from my desk.
In your case...only you can make the call.