We propose a feedback scheme to control the photon statistics in a micromaser/laser cavity, using the system output as the control signal, which generates a highly nonclassical field whose Mandel-Q parameter is even lower than -0.9 and mean photon number much greater than unity. We demonstrate that the so-obtained system constitutes a continuous-wave (CW) quasi-Fock state source, the emission of which exhibits a sub-Poissonian photocount distribution as well as the photon anti-bunching property.