The electromagnetic modes which can propagate in magnetic systems with the linear magneto-electric properties are considered theoretically. The considerations are applied to BaMnF 4. Interactions between different modes, which result from the linear magneto-electric coupling and from the weak ferromagnetic moment are also considered. It is shown that the linear magneto-electric coupling gives rise to the non-reciprocal character of wave propagation, particularly in the spectrum of magnon polaritons.