By using a quantum nonperturbative scattering theory, asymmetry in photoionization of high Rydberg states of rubidium atoms in circularly polarized few-cycle microwave frequency laser pulses was investigated. Asymmetry in photoelectron angular distributions was found. The asymmetry is caused by the quantum coherence of different transition channels. Dependence of the asymmetry on carrier-envelope (CE) phase, pulse duration and photoelectron’s energy were discussed. It is found that the asymmetry varies with the CE phase, pulse duration, and photoelectron’s energy dramatically. The result confirms the recent experimental finding. It provides an effective means to measure the CE phase and control the photoelectron angular distributions in microwave frequency optical regime.