The electrical conductivity, electromagnetic interference (EMI) shielding efficiency, and the morphological and mechanical properties of the polycarbonate/poly(acrylonitrile-butadiene-styrene) (ABS) (70/30)/carbon fiber (CF) composites were studied. The composites were prepared by two different methods, i.e., the pultrusion process and screw extrusion. The composite prepared by the pultrusion process showed higher electrical conductivity of 1.05×101 S/cm and EMI shielding efficiency of 37.6 dB compared to the composite prepared by screw extrusion of 5.20×10−1 S/cm and 6.8 dB at 10 GHz. The increase in the shielding efficiency of electromagnetic wave by 30.8 dB was due to the increased fiber length when the composite was prepared by the pultrusion process. The tensile and flexural strengths of the polycarbonate/ABS (70/30)/CF composite prepared by the pultrusion process were slightly higher by 8.2 and 7.0% compared to those of the composites prepared by screw extrusion, respectively. The above results suggest that the pultrusion process is a superior method to prepare the polycarbonate/ABS (70/30)/CF composites with favorable electrical and mechanical properties.