A prediction model is created and presented in this paper to study the radiation level from mobile telephony base-station antennas using electromagnetic (EM) field simulation. The model concerns only the GSM antennas at 900 MHz. As an example, a residential apartment is chosen to be modeled and simulated using the method of moments, and compared with the on-site EM field measurement. As the three-dimensional model of the apartment has a size of 17.3 λ × 18.28 λ × 10.2 λ and is electrically large, the method of moments with higher-order basis functions and parallel computation are used to reduce the problem size and the computation time. The simulation results of the model shows a good agreement with the measurement results, and thus confirmed the model correctness. Also, based on the created model, the radiation level at any points in the apartment can be predicted and the results illustrated the whole region is within the radiation exposure threshold given by ICNIRP radiation safety standard.