In this paper, we propose a power-efficient scheduling scheme that stochastically minimizes the power consumption of a real-time parallel task while meeting the deadline on multicore processors. The proposed scheme applies the parallel processing that executes a task on multiple cores concurrently, and activates a part of all available cores with unused cores powered off, in order to save power consumption. It is proved that the proposed scheme minimizes the mean power consumption of a real-time parallel task with probabilistic computation amount on DVFS-enabled multicore processors with a finite set of discrete clock frequencies. Evaluation shows that the proposed scheme saves up to 81% power consumption of the previous method.