The structural analysis of masonry arch bridges involves several crucial issues related to the seismic safety assessment, since the application of both static and dynamic nonlinear analyses is not trivial. The reliability of the pushover analysis results is essential since the seismic structural safety is predicted by means of a simplified approach. In particular, the selection of the most significant vibration mode is not straightforward for massive structures. This work delves into several factors related to such analysis techniques, with reference to the case-study of an existing three-arched masonry bridge. First of all, the effectiveness of the nonlinear static analysis is evaluated by means of a comparison with the nonlinear dynamic analysis. Then, the choice of the control node on the FE structural model is investigated, in order to understand its influence on the variability of the results in terms of seismic capacity. Although the top node is usually considered as the most significant point of framed structures global behaviour, in case of arch bridges such a choice may not to be suitable. The critical discussion of the performed numerical analyses gives an important contribution to the understanding of the seismic assessment of the considered structural typology.