We report the nonresonant excitation of the nonstationary holographic currents in an external sinusoidal electric field. The theoretical analysis of the effect has been performed for the conventional model of semiconductor with one type of partially compensated donor level. We demonstrate that the application of an ac field sufficiently increases the photocurrent amplitude. At the same time the frequency transfer function of the effect maintains the form typical for the diffusion mechanism of photocurrent excitation. The dependencies of the current amplitude and characteristic cutoff frequency versus applied voltage are utilized for the determination of the photocarrier's μτ product. The advantages of the proposed technique are discussed. The experiments are carried out in a photorefractive n-type Bi12SiO20 crystal. The signal enhancement of ~50 dB has been achieved and the μτ product is found to be μτ=(0.8-1.2)×10-10 m2/V.