Barring other clues that you have other alignment problems(pulling to one side, excessive dartiness, unusual tire wear, etc,...) the wheel is probably just not centered. If it bothers you then any alignment shop can fix it. If the car has been aligned recently you can probably take it back and request them to fix it.
I noticed as my steering rack bushings were more and more worn out my wheel wouldn't always center as well.
I actually had it aligned a couple months ago, but they couldn't fix the wheel. The alignment on the car is fine, no uneven tire wear. The only strange thing I found was a fairly strong pull to the right when my winter tires were installed. Now that I changed tires, the pull is gone, but the wheel is off center still.