This paper deals with separation flow control over an NACA0015 airfoil using a nanosecond-pulse-driven dielectric-barrier-discharge plasma actuator (NSDBD-PA). In this study, we evaluated the effects of driven frequency of NSDBD-PA on aerodynamic forces and associated flow field at the free-stream velocity of 40 m/s (Reynolds number of 252,000) by conducting force measurement and Particle Imaging Velocimetry (PIV) measurement. The results of force measurement show that the effective value of non-dimensional frequency (𝐹 + ) are different at the post-stall angle (α = 22 deg) and the deep-stall angle (α = 28 deg). The results of PIV measurement show that, at 𝐹 + = 0.25 and α = 28 deg, the vortices generated by NSDBD-PA are combined with the ones from the lower surface and from large-scale vortex structure travelling downstream. It is inferred that vortices pass over the upper surface of the airfoil, resulting in, an increase in lift and drag.