In this paper, we show that it is possible to predict the dielectric loss spectrum of methoxy groups in amorphous poly(vinyl methyl ether) from their rotational energy profiles obtained by a simple quasistatic technique described in our previous paper. Kramers' transition rate theory is used with a slight modification to account for the nonquadratic profiles encountered and short molecular dynamics runs are used to obtain the moment of inertia and rotational frictional coefficient of a methoxy group. The predicted dielectric loss spectrum and its temperature dependence are in good agreement with experimental observations with no adjustable parameters other than those specified in the force field. It is found that the width of the dielectric loss spectrum is essentially due to the spread of activation energies with a negligible contribution from the spread of relaxation time prefactors.