I would be REALLY careful about using a microwave to heat up a towel. Newer microwaves are much more consistent than they used to be, but they can still have hot spots.
You could very easily have a towel that felt just right when you reached into the microwave, but badly scalded your face at a hot spot. Frankly, I'd be more comfortable using boiling water out of a kettle. At least the whole thing would be the same temp, and you could just wait until it cooled enough for your face.