The aim of this study was to electrospun uniform nanofibers with antibacterial properties, to combine them with a high-efficiency particulate air (HEPA) filter material and to determine the filter performance of this composite filter. To achieve these objectives, polyamide 6 (PA 6)/chitosan (CS) blend nanofibers were produced and their antibacterial activity was analyzed. Then PA 6/CS nanofibers were coated on a commercial HEPA filter material and the filter performance of this composite filter was tested. Antibacterial activity analysis indicated that PA 6/CS nanofibers had very good antibacterial activity against both Staphylococcus aureus and Escherichia coli. Nanofiber coating improved the filter efficiency of the HEPA filter. However, it also increased pressure drop. The filter efficiency increased with decreasing nanofiber size in nanofiber coated HEPA filter. Pressure drop did not follow the same trend. First, it decreased with decreasing fiber diameter, but a further decrease in fiber diameter caused an increase in pressure drop. In conclusion, nanofiber size has a great effect on pressure drop and to get high filter efficiency without a substantial increase in pressure drop a careful selection of nanofiber size is essential.