Two finite element models of a quartz AT-cut resonator were employed to investigated the effects of electromagnetic radiation on the resonator Q. The two models employed the governing equations for viscopiezoelectricity and viscopiezoelectromagnetism, respectively. The models showed decreasing Q with frequency increase. The Q of the viscopiezoelectric model compared well with the empirical formula for the Q of quartz AT-cut resonators. At frequencies in excess of 2 GHz, the Q of the viscopiezoelectromagnetic model showed increasing difference from the Q of the viscopiezoelectric model. The electromagnetic radiation loss took up an increasing percentage in the loss of Q with frequency increase in excess of 2 GHz. At 3.3 GHz, it took up about 14% of the loss in Q.