Energy efficiency is a critical issue for battery-driven mobile devices. The popularity of mobile games with increasingly sophisticated graphics raises an urgent need for an online power governor for both CPUs and GPUs. This study proposes an adaptive on-line CPU-GPU governor for games on mobile devices to minimize energy consumption. The concept is implemented on a Google Nexus 7 device and evaluated using real world gaming applications (APPs). The results show an energy savings of up to 26% compared to the Performance governor in Linux (include network, screen, and system idle power) while maintaining a stable user experience.