In this work, we consider a base station (BS) mounted on an unmanned aerial vehicle (UAV) called as an aerial BS (ABS). The ABS is equipped with multiple antennas to assist two pairs of users in nonorthogonal multiple access (NOMA) scheme, and it serves as a relay station to forward the data from the uplink to the downlink of ground IoT users in half-duplex mode. Moreover, the communication power of ABS is harvested from ambient radio-frequency (RF) sources, such as television (TV) and radio signals via the time switching mechanism. In order to improve the efficiency of harvested energy, multiple antennas at the TV/radio tower and the maximal-ratio transmission (MRT) scheme are applied. The proposed ABS RF energy harvesting system overcomes the problem of connectivity of ground IoT users and the energy limitation of devices. The system performance is evaluated in terms of the outage probability of each pair of IoT users in various urban communication environments. Monte Carlo simulation results are provided to validate the accuracy of the developed analytical results and also demonstrate the performance of the proposed system. The results show that the proposed system achieves better performance than that of benchmark systems and the performance can be improved significantly by adjusting the UAV’s altitude.