This study presents a method for monitoring the voltage across the AC capacitor in a grid-connected hybrid active power filter without the use of additional voltage sensors. In the case of an AC capacitor used in a hybrid, active power filter, there is a risk of burnout caused by exceeding the allowable voltage owing to the harmonic current and voltage generated by the inverter. Therefore, this study presents a method to monitor the voltage of the AC capacitor using the current from which the DC component has been removed without any additional voltage sensors to prevent the burn-out of the AC capacitor. The proposed sensorless AC capacitor voltage monitoring method is verified through simulations and experiments. The difference between the magnitude of the voltage measured in the simulations and experiments and the magnitude of the voltage predicted with the proposed method was approximately 0.526[%] on average.