In this study, electrical conductivity and electromagnetic interference shielding effectiveness (EMI SE) of compression and injection molded samples were investigated. Nanocomposites were prepared using melt mixing method by diluting nanofiller masterbatch at different blend ratios. Injection molded samples were prepared by a laboratory mixing molder and also we used a hot press for preparing compression molded samples. Electrical resistivity of samples was measured using a KEITHLEY 2602A System Source Meter®. Both injection and compression molded composites with CNT had lower electrical resistivity than those with graphene. In addition, injection molded samples showed lower R-squared value than compression molded samples that is attributed to the alignment of nanofillers in the flow direction. Interestingly, comparison between hybrid and single nanofiller specimens revealed that incorporation of both CNT and graphene diminishes the degree of filler alignment in the injection molded samples. Moreover, electrical resistivity of hybrid injection molded samples had positive deviation from the mixture law and surprisingly, these samples in some ratios showed a significant synergistic effect. Apart from this, R-squared value of hybrid injection molded samples was equal to their compression molded counterparts which their I-V behavior was in accordance with the Ohm’s law. The increase in the R-squared value of hybrid than CNT injection molded sample is ascribed to the connections between CNT and graphene particles. Furthermore, the EMI SE measurements were conducted by a Network Analyzer in the X-band frequency range. EMI SE of graphene composites was lower than CNT composites and both of injection and compression molded samples showed synergistic effect. FE-SEM images and rheological measurements confirmed the formation of a network between CNT and graphene particles which is thought to be responsible for decreasing nanofiller alignment in injection molded samples.