In this paper, an OS level power estimator based on monitored system events for multimedia mobile devices is presented. The OS level power estimator periodically obtains significant-events count values and calculates power-consumption estimations through mathematical models. We have implemented this power estimator in a Linux kernel and evaluated it while running a video decoder application on an embedded development platform. Experiments results show that the accuracy of power estimations is high with regard to the real measured power consumption, i.e., the error between them is less than 1% in average.