We investigate the effect of hyperfine interaction on magnetoresistance in nonmagenetic organic semiconductors. A Lorentz-type magnetoresistance is obtained from hyperfine interaction-dependent spin precession picture. The magnetoresistance depends on initial spin orientation of electron to hole in electron-hole pairs. Increasing hyperfine interaction slows down change of the magnetoresistance with magnetic field. The field dependence, the sign and saturation value of the magnetoresistances are composite effects of recombination and dissociation rate constants of singlet and triplet electron-hole pairs.