We study the efficiency of frictional thermal ratchets driven by a finite frequency driving force and in contact with a heat bath. The efficiency exhibits varied behavior with driving frequency. Both nonmonotonic and monotonic behavior have been observed. In particular, the magnitude of the efficiency in the finite frequency regime may be more than the efficiency in the adiabatic regime. This is our central result for rocked ratchets. We also show that for the simple potential we have chosen, with only spatial asymmetry (homogeneous system) or only a frictional ratchet (symmetric potential profile), the adiabatic efficiency is always more than in the nonadiabatic case.