Using the framework of the density functional theory (DFT), we calculate the electronic, magnetic and structural properties of TbO in its three possible crystal structures: rocksalt (RS), cesium chloride (CsCl), and zincblende (ZB). The full potential linearized augmented plane wave (FP-LAPW) method within the local spin density approximation (LSDA) and generalized gradient (PBE-GGA) approximations are used. Magnetic and nonmagnetic (NM) calculations are used and a modified version of Becke and Johnson (mBJ) exchange potential has been used to calculate the band gaps. We discovered that though TbO is stable in a ferromagnetic (FM) state, it is stable in the rocksalt phase in its ambient manifestation. Both the LSDA and PBE-GGA calculations reveal that the three structures are metallic. However, using the mBJ calculation, it is clear that the RS and CsCl phases of TbO compound are metallic, while the ZB phase is an insulator in the spin up case and is a semiconductor in the spin down case at ambient pressure