In a large scale WSN deployment, reprogramming the WSN nodes with new firmware using In-System Programming (ISP) by opening the enclosure of WSN node will be a tedious job. Instead, reprogramming could be achieved by providing physical access to JTAG/SWD on the enclosure; but it will compromise the Ingress Protection (IP) rating of WSN node. Hence, Wireless based In-Application Programming (IAP) could be preferred. Near Field Communication (NFC) is a secure and promising short distance radio communication technology. This paper presents how an NFC transceiver can be utilized to program the microcontroller of WSN nodes. It also explains the development of boot loader program for WSN node to support wireless based IAP.