The present disclosure is directed to a method for detecting a mass imbalance in a rotor of a wind turbine. The method includes receiving, with a computing device, sensor data indicative of an operating characteristic of the wind turbine. The method also includes determining, with the computing device, a mean amplitude of a designated frequency component of the operating characteristic. Furthermore, the method includes determining, with the computing device, when a mass imbalance is present within the rotor based on the mean amplitude of the designated frequency component.