This letter reports the optimal solution for microwave hyperthermia. Conventionally, the operating frequency of the hyperthermia has been chosen as one of the industrial, scientific, and medicine radio bands. For the selected frequency, the excitation of multiple discrete sources for hyperthermia has been optimized via various classical computing algorithms. In contrast, this letter includes the operating frequency in the list of optimization parameters. For eight evenly-distributed dipole sources around the body, it turns out that the optimal frequency lies in a few hundred MHz. Furthermore, we report that such an optimization can be accomplished with quantum annealing. The accuracy of quantum annealing is validated with the classical counterparts. This work reveals the potential for expanding the application of quantum annealing into the field of electromagnetic engineering.