The moving photocarrier grating (MPG) technique for the determination of the carrier mobilities and the recombination lifetime of $alpha$-Se:As films has been studied. The electron and hole drift mobility and the recombination lifetime of $alpha$-Se films with arsenic (As) additions have been obtained from measurement of the short circuit current density $j_{sc}$ as a function of grating velocity and spatial period. The hole mobility decreases due to defect density of hole traps when x exceeds 0.003, whereas the hole mobility increases for the case of low As addition (x$le$0.003). We have found an increase in hole drift mobility and recombination lifetime, especially when As with (x = 0.003) is added into the $alpha$-Se film.