The author investigates the stability of a magnetized non-isothermal (Te ≫ Ti) plasma in an alternating electric field when the field frequency Ω0 is close to the frequency of the ion-sound oscillations of the plasma. The amplitude of the oscillatory velocity of electrons in a h.f. field is assumed to be small compared with their thermal velocity (u0 ≪ vTe ). It is shown that, for perturbations with wave number kz satisfying the resonance condition there exists in such a plasma an instability with a growth rate . The width of the instability zone is determined in the kinetic and hydrodynamic approximations. In the hydrodynamic approximation, if one does not allow for dissipation, there is instability however small the value of . If one allows for collisionless kinetic damping of the oscillations on the electrons, the instability develops only when u0 exceeds come critical value ∼ vTe (me/Mi)¼.