As long as your main breaker panel is sized at 100 amps, it is fine. Check the main breaker. The power company may of just ran larger wire in-case your house is upgraded to 200 amps.

Just to clarify, all the wiring in your house should be protected by a breaker. The breaker should be sized so that it trips if the current goes above what the wiring can handle. In your case, if you have a wire that can handle 100 amp and a breaker that trips at 100 amp, then it is perfectly safe. If you have wiring that can handle 100 amp and the breaker isn't going to trip until 200 amp, then it would be dangerous.

A slightly larger concern for a home buyer is that the service is only 100 amp. That is undersized by modern standards. If the house is older, it was probably perfectly reasonable at the time, but people have so many more electric appliances and electronics then they used to - microwave, toaster over, blender, coffee makers, toaster, dishwasher, disposal etc - and that is just in the kitchen. Depending on how your family lives, you may or may not need to upgrade the electrical.

All good points. My new a/c needed an additional 60amps. so, 100amps [total] kind of tells me that you a>don't have an a/c or b> you have a very old a/c.