We apply the average electron model to describe high harmonic generation in a collisional plasma in a laser field. The model is based on the coupled kinetic equations for electron velocity and electron temperature. The harmonic intensities are obtained from the Fourier coefficients of the nonlinear part of the electron velocity. Numerical calculations are reported for both strongly and weakly ionized plasmas in the nonstationary regime. We show the role of collisions frequencies as well as of quiver and thermal velocities in the harmonic generation efficiency.