Tar-rich coal has been an attractive resource in recent years. Underground radiofrequency (RF) heating, a potential technique, could develop tar-rich coal resources in an eco-friendly way. Temperature evolution and distribution are critical to coal exploration. This study proposes a numerical model to investigate the thermal performance of tar-rich coal during RF heating. The finite element method solves coupling equations between electromagnetic (EM) wave propagation and heat transfer. The consistency of the numerical simulation with the experimental test demonstrates the proposed model. Numerical results show that the heat concentrates near the vicinity of the RF antenna due to the attenuation of EM waves and the low thermal conductivity of coal. A field-scale simulation shows that the effective heating range of coal would reach 2.5 m using a 20 kW and 915 MHz wave source after 200 d. Parametric studies indicate that the effective heating zone enlarges with the wave frequency. As the frequency increases, the effective heating range extension becomes indistinctive.