How can I get a shock from a circuit when the breaker is off?
Well, if there is something leaking current onto "ground" and that thing is connected to your metal box, and the metal box is not connected to the ground in your breaker panel, no, that's not great.  I would take a multimeter, turn off the breaker to the house, and check the resistance between neutral and the box.  If it is large, then they are not not bonded together at the panel, but yet something somewhere is connecting them in your house.  Try using a 3-prong tester on some outlets in your house and see what results you get.