This depends on how you use your treadmill. Obviously, running will use more power than walking. Doing intervals will use more power than running at a constant speed, as well as being a heavier person.
But, the short answer is yes, treadmills use a lot of electricity. They are not an environmentally friendly way to exercise.
If you care about the power bill, and the environment, you’re far better off sticking to a manual treadmill, or another resistance-based machine like a stationary bike.