Magneto-rheological elastomers (MREs) are a class of smart materials which can adjust their modulus or stiffness by an applied magnetic field. Thus, MREs can be used as controllable stiffness elements in various engineering systems. In order to use them for engineering applications, characterizations of MRE behaviors under magnetic fields and developments of dynamic models (such as a phenomenological model) that can capture the behaviors must be studied well. This paper focuses on modeling of MRE samples under shear deformation, which is a common mode of operation of MRE materials in structural engineering. It proposes a dynamic model that combines the Ramberg-Osgood model and the Maxwell model. The model is validated using experimental characterization test data. The results show that the proposed dynamic model can be effectively used for predicting the dynamic behavior of MREs under shear deformation.