A large number of masonry arch bridges exist within the Iranian railway network, many of which are more than seventy years old. In recent years, not only has the demand for freight transport increased, but the introduction of high-speed trains has also become a critical issue for the national railway system. Due to the complexity involved in modeling such bridges, conducting dynamic tests is essential. The dynamic test performed on the Akbarabad Bridge, located at kilometer 24 of the Tehran–Qom railway line, provided key information including the bridge’s natural frequencies, vertical accelerations, and vertical displacements under train passage at various speeds. Given the importance of the problem and the need to accurately determine the bridge’s dynamic characteristics, developing a reliable numerical model under dynamic loading was necessary. Accordingly, based on the measured data, a finite element model of the bridge was constructed. The geometric properties were modeled according to the available plans, and due to the predominantly two-dimensional behavior of the structure under vertical loading, a plane strain analysis was adopted. To update the model, the natural frequency was selected as the calibration parameter. After calibration, the bridge response in the frequency domain was evaluated by applying the train load in a harmonic form. The results indicate that the bridge response is strongly dependent on the frequency content of the train-induced dynamic loading.