Not if it's a tank system. They can, but they don't have to, since the pilot stays lit all the time. A tankless system has to use some power since it cycles every time you use it.
Some use a 9v battery on their starter.
Regardless, you can just use a match if you want to.
In either case, they don't require mains power.
(Sure, there are different models, etc. but it's not a requirement that all have an electric start, or a mains electric start)