Islanding detection plays a very important role in the design of a protection system for distributed generation (DG). The conventional methods face problems during the perfectly matched balanced load condition of DG as there is no significant change in voltage and frequency. In this paper, an active islanding detection method is proposed which perturbs the DC link voltage of DG, actuated when there is a sudden rise in the total harmonic distortion (THD) of the system greater than 4%. This perturbation again increases the level of harmonics if the DG is islanded as the grid loses control over DG. Thus, the increase in harmonic level is utilized as an indication of islanding. During normal mode, the grid offers a low-impedance path to harmonics and, thus, the harmonic level is maintained. The testing of islanding is done with the help of a MATLAB model of grid-connected DFIG-based wind farm. The proposed method can be a potential method for detecting islanding of inverter-based DGs during worst cases and also for knowing the mode of operation of DG, when implementing adaptive protection.