We consider a nonlinear elliptic-parabolic system modelling induction heating processes when a sinusoidal electromagnetic field is applied at the boundary of the inductor. The magnetic field satisfies an elliptic equation whereas the temperature equation is parabolic. These equations are coupled together due to the conductivities and the Joule effect. We show the existence of a weak solution to the corresponding problem and under additional assumptions, we study the uniqueness of the solution.