A layer of electrically conducting couple-stress fluid heated from below in porous medium is considered in the presence of uniform horizontal magnetic field. The medium permeability hastens the onset of convection whereas the magnetic field and couple-stress postpone the onset of convection, for the case of stationary convection. The oscillatory modes are introduced by the magnetic field which were not present in the absence of the magnetic field. The overstable case has been considered and a sufficient condition for the non-existence of overstability is obtained.