We obtained the 3D crustal velocity structure of the Central Alborz region in northern Iran using local earthquake tomography. We used P-wave arrival-time data recorded by stations from three national observatories consisting of the Iranian Seismological Center, the International Institute of Earthquake Engineering and Seismology, and the Tehran Disaster Management and Mitigation Organization along with data from a temporary network. The P-wave arrival-times from local earthquakes have been used to produce a 3D tomographic velocity model of the Central Alborz using the inversion code SIMULPS. The low-velocity sedimentary layer in the upper crust is up to ~4 km thick. Our results show a mid-crustal interface at ~15 ± 2.5 km depth. This interface shows a pronounced uplift at a relatively aseismic part of the Mosha fault that might have the potential to produce an earthquake with magnitude Mw ~ 6–6.5. Independent gravity modeling was carried out, which confirms the location of the anomaly at the relatively aseismic part of the Mosha fault. A small uplift of the mid-crustal interface beneath the junction of the Mosha and North Tehran faults close to the city of Tehran might indicate a similar anomaly. Various resolution and synthetic tests (e.g., checkerboard, Resolution Matrix Diagonal, and data uncertainties) were performed and support the reliability of the resolved anomalies.