Step motors generate eddy current losses by simply turning; the faster they turn, the greater these losses. Here's a fun experiment:
Chuck a step motor shaft in a drill press. Set a drill press to high RPM. Fix it so the motor wires aren't touching each other. Turn the drill press on and spin the motor shaft. Go away for 15 minutes.
When you come back, see if you can touch the motor without getting your fingers burned. The motor wires weren't touching each other so you know there was absolutely no current flowing in the motor windings. What made the motor hot? Eddy currents were induced in the motor stator by the rotating magnet that forms the motor's rotor. These currents circulate in the steel laminations and generate resistive heating in the steel.
A fast turning step motor gets hot even without a drive attached.:-)