In order to study the effect of the frequency and the intensity of high-frequency alternating-current (AC) electric fields on lean combustion, the effects of high-frequency (5-30 kHz; 5 kV) and high-voltage (0-5 kV; 15 kHz) AC electric fields on lean (excess air ratio 1.2/1.4/1.6) premixed CH4/N-2/O-2 flames are evaluated experimentally in the paper in detail. Results show that the mean flame propagation speed increases with the electric field frequency at first. However, the transition frequency, after which the mean flame propagation speed reaches to the maximum and then tends to be stabilized, is shown to be around 25 kHz. The combustion peak pressure increases minimally at various frequencies, but the timing of it decreases apparently; additionally, the effect of frequency on the combustion pressure change is very close to that on the mean flame propagation speed. The initial duration and main duration also have a similar tendency with the increase of the frequency. Besides, with the increase of the applied voltage, the mean flame propagation speed increases nearly exponentially. Meanwhile, the combustion peak pressure increases, and the timing of it decreases. Similarly, the effect of applied voltage on the combustion pressure change is also close to that on the mean flame propagation speed, and the initial duration and main duration also declines with the increase of the applied voltage. The result shows that the combustion of lean mixtures can be enhanced effectively by high-frequency (5-30 kHz) and high-voltage (1-5 kV) AC electric fields, which has a positive meaning in the further study of the electric-field-assisted combustion theory.