In this paper we present our recent studies on the crystal, magnetic and dielectric properties of the β-NaMnO2. Experimental results of neutron powder and electron diffraction combined with measurements of the dielectric permittivity suggest that the β-ΝaMnO2 is an excellent candidate for studying the coupling between the magnetic and electric degrees of freedom. Neutron powder diffraction data reveal the existence of a commensurate and an incommensurate magnetic structure at 200 K and below 100 K, respectively. Dielectric anomalies which appear at the temperature regions where the two magnetic structures emerge, indicate the appearance of magnetodielectric coupling.