Magnetic bearings can compensate spindle motion errors caused by unbalance and disturbance forces because of their active motion control capability. Moreover the magnetic bearings are free from friction and can be used in a vacuum so that they can be candidates for high accurate and high-speed bearings in the future. However few magnetic bearings of nanometer rotational accuracy have been reported. The goal of this research is to realize a magnetic bearing which has rotational accuracy of several manometers at a high speed. First, this paper introduces a precision magnetic bearing in which the radial two-degree-of-freedom motion of the spindle is controlled by electromagnets. Then a partial bias current control of the electromagnets is proposed to reduce heat generation of the electromagnets with high rotational accuracy. Finally experimental results show that the radial magnetic bearing using the partial bias current control can achieve the rotational accuracy of about 10nm (3σ) below 500min-1 without large heat generation.