Magnetoelectric effect in composite materials results from the combination of piezoelectric and magnetostrictive effects. This paper focuses on the development of a harmonic finite element formulation for such coupled problems, taking into account the nonlinearity of magnetostrictive behavior. An application to a magnetic sensor operating under dynamic excitation is presented in order to illustrate the formulation. The enhancement of the magnetoelectric coefficient when a low amplitude harmonic field is superimposed to the static field to be measured is shown to be related to the nonlinearity of magnetic and magnetostrictive behavior.