Silver nano-particles, that were either attached on granular activated carbon or dispersed in a liquid solution, were applied to investigate the removal efficiency of airborne bacteria. The antibacterial experiments were performed by changing the gas residence time in a GAC filtration column and a scrubber module. The GAC filter experiment showed that the antibacterial efficiency declined with time at a gas residence time (RT) of 0.02 second, and the bacterial quantity in the outlet of the column exceeded that of the inlet after 30 hours of operation. However, when using Ag-GAC, the removal efficiency was higher than that of the GAC, and it was maintained over a 3-day period. The experiment results at different gas RTs of 3, 1.5 and 0.5 seconds also showed that Ag-GAC had higher antibacterial efficiencies. The low antibacterial efficiency at a short RT indicates that a careful consideration needs to be implemented for the design of indoor air purification devises. In the scrubber experiment using distilled water, a removal efficiency of 50% was observed initially; however, it declined gradually and the outlet bacterial quantity was even higher than that of the inlet. This result was mainly due to the accumulation of bacteria in the recirculating solution. Contrarily, another scrubber experiment using silver nano-particle solution showed that an antibacterial efficiency of 66% was maintained over a 3-day period. Silver nano-particles were able to minimize the growth of microorganisms in the spray solution, and it resulted in an improved and stable efficiency for the airborne bacterial control.