We investigate the number of parts modulo m of m-ary partitions of a positive integer n. We prove that the number of parts is equidistributed modulo m on a special subset of m-ary partitions. As consequences, we explain when the number of parts is equidistributed modulo m on the entire set of partitions, and we provide an alternate proof of a recent result of Andrews, Fraenkel, and Sellers about the number of m-ary partitions modulo m.