Several applications of optical micromirrors need synchronization of its mechanical oscillation with an external control signal. Self-sustained oscillation of micromirrors is a prerequisite for achieving such synchronization. To suppress its mechanical deformation these micromirrors are operated under atmospheric or controlled pressure environment. Operation under this environment leads to increase in driving voltages to achieve required deflections. However, significant parasitic crosstalk due to these high driving voltages presents a challenge for achieving their self-sustained oscillations. In this paper, stable self-sustained oscillation of a 13.5kHz micromirror is achieved at atmospheric pressure by actively suppressing its crosstalk. Frequency stability of 7.2ppm is obtained for this micromirror's self-sustained oscillation at atmospheric pressure.