Due to the special properties of electrospun nanofibers such as high surface area and porosity, ease of surface functionalization, low pressure drop, suitable mechanical strength, their application in the fabrication of air purifying filtration media has increased dramatically in the recent years. The release of nanomaterials from electrospun nanofibers and human exposure to these substances is one of the concerns regarding to application of nanofiber media in air purifying applications. The aims of present study were to fabricate and characterize the nanofiber filter media, and to determine the release of nanomaterials from them during their application in a filter test rig for removing potassium chloride (KCl) nanoparticles. Polyacrylonitrile, one of the most commonly used polymers in electrospun nanofiber filter media, was embedded with various nanomaterials including magnesium oxide nanoparticles and single wall carbon nanotube and was converted to nanofiber filter mats via electrospinning process. The air samples were collected at the downstream of prepared nanofiber filter mats using polycarbonate (PC) and mixed cellulose ester (MCE) filters according to NIOSH methods 7404 and 7402. The PC filters were analyzed by FE-SEM microscopy for assessing potential release of nanofibers and MCE filters were analyzed by CytoViva's Hyper Spectral Imaging System coupled with Enhanced Dark Field Microscopy (HIS-EDFM) for assessing the potential release of nano materials (SWNTs and MgO NPs) from the electrospun nanofiber filter mats. The findings indicated that electrospun nanofibers and their embedded nanoparticles were rarely detached and released from the filter media during normal filtration process. Therefore, it is possible to obtain a very low release by improving quality of the nanofiber filter media and applying a safe design approach.