For micromirrors used in optical MEMS, in addition to the static displacement-voltage characteristics, the accurate transient characterization of these devices is becoming increasingly important. The latter one is strongly affected by the viscous damping of the surrounding air. A complete analysis of the dynamic behavior should consist of coupled transient simulations including electrostatics, stress, deformation, and fluidics of the air. This paper presents for the first time results of such fully coupled 3D simulations. CFD-ACE+ multi-physics simulator from CFDRC was used for both the static and transient analysis of an electrostatically actuated micromirror. The pull-down voltage was calculated very accurately. The micromirror dynamic response to step voltage varies for different ambient pressures. Air damping is clearly visible in the higher pressure, and it can be optimized in a real design to minimize the settling time of the optical switch.