It certainly can be, particularly if you're sitting at a desk that doesn't adjust so it suits you. Being tall I find most desks are designed for shorter people and it can be a struggle to adjust anything to a point I'm comfortable. I had terrible trouble at my last permanent job because the health and safety requirements for workers who sit include endless lists of how chairs should be adjusted, and yet it wasn't possible for me to achieve such a position because my desk wouldn't rise high enough. But because of the increasing insistence on open plan offices, desks tend to be part of a longer setup so adjusting the height of one isn't an option. That left me in a place where health and safety requirements dictated I needed to adjust my chair in a way that wasn't possible, but the health and safety manager didn't see it as a problem.
I used to get up and stretch my legs every hour or two, I used to make sure I took my full lunch hour, and basically did pretty much anything I could to break up the time I spent sitting. When I clocked that smokers were allowed to take a 5-10 minute cigarette break several times a day I figured I'd take a 5-minute break once in a while too.