A split-ring-resonator-based active metamaterial was investigated for manipulating the spatial intensity profile or wavefront of transmissive waves. In this work, varactor diodes were mounted at gaps in split-ring resonators to electrically control the waves. The fabricated active SRRs exhibit an ON/OFF ratio of 15 dB and a change in the transmission phase of 40o/layer by applying voltage to the varactor diodes. Measurement of intensity modulation revealed modulation speed of more than 20 MHz, in which the change in the intensity of 15 dB was the same as that for static condition.