A bias circuit includes first and second bipolar transistors, first and second field-effect transistors, and a filter circuit. The first field-effect transistor supplies a bias signal to an amplifier. The filter circuit is connected between a collector terminal of the first bipolar transistor and the ground through a base terminal of the first bipolar transistor. The filter circuit has frequency characteristics for attenuating a high frequency component of an RF signal to be input to the amplifier.