There are a few iron deposits in the north and northeastern part of Semnan city that none of them has a systematic exploration background. Ojat_Abad deposit is one of them located in 63 km of north-east of Semnan at the southern side of Semnan - Damghan main road. A magnetic survey including 1200 measuring points has been recently performed to explore the deposit within an area of 89 acres. The prepared total and residual magnetic field maps clearly demonstrate the existence of iron anomaly at seven locations in a zone with northeast - southwest trend. In this paper, attempt has been made to obtain more qualitative and quantitative information for the recognized anomalies by performing two and three dimensional (2D, 3D) numerical modeling. To achieve the goal, the residual anomaly map, obtained by professional software called Modelvison Pro is used. It was found that the results of 2D and 3D modeling confirm each other in the most cases and in addition are in quite good agreement with the results of existing mining excavations. The obtained results also demonstrate the explored anomalies locate separately, and except one of them, all are located at a depth less than 35 meters.