The electrical potential of an object is determined by providing a mechanically oscillating electrode located at a distance from the object and making the electrode mechanically oscillate. A change in a state of electric charge of the electrode over time and amplitudes of at least two frequency components during the change in the state of electric charge over time are determined. Based on the amplitudes, at least one parameter that forms part of the value of a capacitance of an arrangement formed by the electrode and the object is determined, so that the capacitance of the arrangement formed by the electrode and object can be determined based on the parameter. Finally, the electrical potential is determined from the change in the state of electric charge and the capacitance.