This letter introduces a method for implementing a frequency-reconfigurable Fabry-Pérot cavity (FPC) antenna utilizing polarization standing waves (PSWs). The PSW is supported by two metasurfaces (MSs) at cavity ends. The resonant condition allows the antenna to have frequency-reconfigurable characteristic by mechanically rotating the top MS around the center and relative to the bottom MS, without adjusting the physical dimension. The antenna is prototyped at 60 GHz for millimeter-wave applications. Simulated and measured results demonstrate that a tunable frequency range of 60.8-66.2 GHz with a maximum boresight gain of around 22.2 dBi can be attained, verifying the antenna concept.