Yes, it is normal to be able to "back-drive" the motor by turning the gear when it is 'unplugged'.
When it is 'plugged in and calibrated', if you try to back-drive it, it will usually fight against you. In some cases the motor goes to 'sleep' and it might not immediately 'wake up' to fight against you (but it will wake up and go to the right focus point immediately if you move the hand controller knob).
Does this sound like what you're experiencing? If so, nothing to worry about!