The shielding technique by active coils is proposed to mitigate the magnetic field produced by a wireless power transfer (WPT) system based on near field coupling. General guidelines are provided for the active shielding design to shield the source for emission reduction or to shield the victim for immunity enhancement. Then, a method is proposed to identify the suitable excitation of the active coils. The proposed method permits the mitigation of the magnetic field in a specific point or of the induced effects in a loop area. Furthermore, the influence of the active shielding on the performance of a WPT system is also investigated. Finally, the proposed solution for active shielding is validated by measurements. A shielding effectiveness (SE) of about 20 dB on the considered area is obtained with a negligible degradation of the WPT system efficiency.