Mechanisms of stationary and nonstationary interactions of a metal shaped charge jet with the frontal (moving backward) and back (moving forward) plates of the explosive reactive armor are considered. A range of interaction parameters, at which these mechanisms are implemented, is defined. It is shown that interaction of the jet with the frontal plate is stationary in general and leads to the jet erosion in the transverse direction (i.e., reduction in diameter) and its deflection by a small angle. The interaction between the jet and the back plate is mainly of nonstationary discrete nature and produces the one-sided transverse perturbations in the jet, which, while evolving, lead to curving and the subsequent destruction of the jet.