In this work, we evaluate the basic properties of carbon nanofiber composites that are intended for use in electromagnetic interference (EMI) shielding material. The material was manufactured by adding BaTiO3 or Fe3O4 nanoparticles to carbon-based nanofibers via electrospinning and carbonization. The nanofiber composites were characterized via scanning electron microscopy, transmission electron microscopy, X-ray diffraction, Raman spectroscopy, and an LCR (inductance, capacitance, and resistance) metering. The polyacrylonitrile (PAN) nanofibers used as the carbon fiber precursor changed to carbon nanofibers via carbonization, and their diameter decreased during this process. The electrical conductivity of the nanofibers increased as the amount of BaTiO3 nanoparticles increased, and the carbon nanofiber was cut short by the aggregation of the Fe3O4 nanoparticles after carbonization, which resulted in a decrease of the electrical conductivity.