Depends on caliber, bullet weight, velocity, and the height of your scope rings (actually the distance between the center of your barrel and the center of your scope tube).
As a general rule, you would have to aim slightly high - about 1 inch high for an average type rifle at 25 yards. If you have a 223 with a high scope mount you would have to aim about 2 inches high at 25 yards.
Note that is for a 100 yrd zero.