In this paper, uneven temperature distribution of a heated material is computed by a coupled method considering the change of the complex relative permittivity by the temperature rise. The coupled method can calculate electromagnetics, and all of the heat transmission phenomena of heat conduction, heat transfer by air convection, and heat radiation. The calculated temperature distribution at the surface of a material is compared with the measured one. As a result, the calculated and measured temperature distributions agrees well. The validity of the proposed method on this kind of problem is verified.