An ER material composed of alumino‐silicate particles in paraffin oil is studied for its response to sinusoidally oscillating shear strains at frequencies in the range of 10–50/s. The response of the material may be discussed in terms of three rheological regions; pre‐yield, yield, and post‐yield. Within each region there is a different mode of deformation; viscoelastic in the pre‐yield, viscoelastic plastic in the yield, and plastic in the post‐yield. The deformation modes are dependent on applied electric field strength, strain amplitude, and strain frequency. Furthermore, the energy dissipated by the ER material is analyzed as related to strain amplitude and electric field. The energy dissipated by the ER material is proportional to the strain raised to the second power when the material is deformed in the pre‐yield region, varies between the strain raised to the second power and raised to the first power during deformation in the yield region, and the energy is proportional to the strain raised to the first power when deformation occurs in the post‐yield region. Finally, a rheological model is introduced to account for the behavior of ER materials qualitatively.