An ion thruster emits a high density plasma plume and the electromagnetic noise radiated from the plasma current may affect the spacecraft instrument. An electromagnetic particle simulation code has been developed to investigate the effects of the electromagnetic interference induced from the ion thruster plume. The electromagnetic waves are excited due to plasma instability caused by strong polarization field inside imperfectly neutralized plume. The strength and frequencies of electromagnetic noise radiated by ion thruster plume depend on the distribution of charged particles inside the plume, static magnetic field strength and its orientation.