A theoretical model of the conductivity of a thin metal layer in a longitudinal constant magnetic and alternative electric field in the view of diffuse-specular boundary conditions is constructed. An analytical expression is obtained for the integral conductivity as a function of dimensionless parameters: layer thickness, electric field frequency, magnetic field induction and surface specularity coefficients. The dependences of the layer conductivity on the above mentioned parameters are analyzed. The results are compared with known experimental data.