A security system may include an access control device associated with a personnel access position. The access control device may include a first Near-Field Communication (NFC) sensor, and a first controller configured to selectively grant personnel access based upon receiving a valid security code from the first NFC sensor, and to deny personnel access and generate an access denial electronic message(s) based upon receiving an invalid security code from the first NFC sensor. The system may also include a mobile wireless communications device(s) including a second NFC sensor and a second controller, which may be configured to communicate a security code via the second NFC sensor to the first NFC sensor based upon proximity therewith, and to receive a corresponding access denial electronic message from the first controller based upon the security code being invalid.