The paper deals with a mathematical model of electrostatic MEMS (Micro-Electro-Mechanical Systems) actuator with an associated mechanical system. The model mimics the behavior of a commercial MEMS-driven micromirror. It is shown that the electric port of the electrostatic comb drive can be correctly modeled as a generic memcapacitor whose state equation describes the dynamic behavior of the cooperating mechanical subsystem. The so-called narrow-band frequency-dependent hysteresis, associated with such types of MEMS, is analyzed.