That can happen if you change the stock focusing screen to a third party one. The replacement screen may be too thick or too thin in cross section or if an incorrect shim is used.
But if you're using the stock focusing screen and it coincides with what the sensor records as sharp, then there really can't be such a thing as back or front focusing because any focus error lies with the operator.
Anyway the first thing I suggest is to make sure the viewfinder diopter correction is set to your eyesight first before you do anything.