No, it currently is at an altitude of 426km (was at 423km when I started writing), the orbit isn't at a fixed altitude though, it varies, and the residual atmosphere causes drag which means every once in a while the orbit has to be adjusted.
My favorite fact about the ISS is that it actually has an engine to do its own orbital boosts. Astronauts have taken videos where they slowly drift from one side of the cabin to the other during a burn