The dynamic behavior of a clamped–clamped microbeam loaded by a symmetric combined voltage, which is composed of a direct current (DC) voltage and an alternating current (AC), is investigated in this paper. Based on the Euler–Bernoulli hypothesis and the standard anelastic solid model, the equation of motion of this microbeam with considering the material damping is got, and then by using the Galerkin method a reduced-order model is derived. An instability phenomenon named as electromechanical dynamic buckling in this system is shown, and the condition of instability is determined by the averaging method. To validate our results, a numerical simulation model is set up. The effects of the fringing field, residual stress, applied DC voltage, environmental damping and material damping on the electromechanical dynamic buckling are discussed.