Nanocomposites of Polycarbonate (PC)/Multiwalled Carbon Nanotubes (MWCNTs) containing 0.5 to 3 wt. % MWCNTs were prepared via two methods of melt mixing and solution mixing. The effect of CNT content and processing methods on electrical and electromagnetic properties of nanocompoite samples were investigated. Electrical measurements indicated an electrical percolation threshold of less than 1 wt. % of CNTs for this system. It was found that PC/MWCNTs composites prepared by solution method exhibits a lower electrical resistivity and a lower electrical percolation threshold in comparison with those prepared by melt mixing. The electromagnetic shielding interference measurements (EMI) in the X-band (8.2 to 12.4 GHz) indicated that the electromagnetic properties are increased by increasing the amount of CNTs and the specimen thickness. Also it was observed that the composites prepared by solution method, have higher shielding efficiency (SE) values. Finally in order to reach an acceptable value for commercial applications of EMI shielding materials (20 dB), thicker samples were produced. It was found that the 3.5 mm thick sample containing 2 wt. % of CNTs has a 20 dB shielding effectiveness and the main mechanism of shielding is absorption. Keywords: Electromagnetic Interference Shielding, Electrical Conductivity, Melt mixing, Solution mixing, MWCNTs, Polycarbonate.