This is an essential question; so, do not take it lightly for the sake of your health and the pump. Before you perform any servicing of any kind on your pool pump, you first need to ensure that it is unplugged and free from any electricity. Just as you never want to deal with live currents in your home when you are messing around with electrical circuits, you want to avoid servicing a pump with electricity flowing into it.
If you have it drilled into your mind that you will be safe and do not think it is necessary to unplug the unit, change your mindset. No matter if you are a serviceman by profession; one wrong move could result in injury or possibly death due to electrical shock.