A novel electro-rheological model for liquid and solid dielectrics is presented, which is well adapted to the purposes of engineering calculations. The study is focused in the frequency range of relaxation processes, well below the optical range. In addition, the dielectric material is considered to have only polarization charges, i.e. conduction charges are absent. The description for the energy transfer processes in dielectric materials is based on one-dimensional approximation using a rheological model with two- and three- parameter Voigt elements. The mean field approximation is adopted, considered as an averaging of the mechanical and electrical properties for the dipole and inter-dipole spaces. The continuity condition for mechanical and electrical forces is also taken into account. The model was applied to the study of ethylene-propylenedyene monomer (EPDM) commercial rubber having two phases, amorphous and semi-crystalline. A good agreement was found with the experimental results from dielectric relaxation and dynamical mechanical measurements