Discharge under open-circuit conditions may be often used to find the drift mobility of charge carriers in thin films of low-mobility materials. The existing theories of the discharge assume domination of charge transport in the conduction band. In order to find whether the theories may be used for interpretation of experimental results in hopping systems a computer simulation was carried out. It has been shown that direct usage of the existing theories may lead to wrong values of drift mobility found from the discharge. The method of estimation of real value of mobility in the temperature range 100-500 K for various values of the decay parameter of the electron localized wavefunction and for various standard deviations of the energetic distribution of the localized states is presented in this paper.