Radio‐frequency plugging and heating of a magnetized sheet plasma has been studied both experimentally and theoretically. It is confirmed that a sheath resonance related to ion motion occurs at a frequency intermediate between the ion cyclotron frequency and the lower hybrid frequency, and an anti‐resonance occurs at the lower hybrid frequency. The rf electric field in the plasma, which produces a ponderomotive force on the ions, is strongest at the sheath resonance, and is used for the nonadiabatic rf plugging of the magnetized sheet plasma in a mirror field. The ion heating process is explained by Joule heating due to the rf electric field.