Zigbee IoT devices have limited computational resources, including processing power and memory capacity. Therefore, because of their complicated computational requirements, traditional encryption techniques are inappropriate for Zigbee devices. Because of this, we proposed a novel, “lightweight encryption” method (algorithm) is based on “DNA sequences” for Zigbee devices. In the proposed way, we took advantage of the randomness of “DNA sequences” to produce a full secret key that attackers cannot crack. The DNA key encrypts the data using two operations, “substitution” and “transposition”, which are appropriate for Zigbee computation resources. Our suggested method uses the “signal-to-interference and noise ratio (SINR)”, “congestion level”, and “survival factor” for estimating the “cluster head selection factor” initially. The cluster head selection factor is used to group the network nodes using the “adaptive fuzzy c-means clustering technique”. Data packets are then encrypted using the DNA encryption method. Our proposed technique gave the best results by comparing the experimental results to other encryption algorithms and the metrics for energy consumption, such as “node remaining energy level”, key size, and encryption time.