Yttria-stabilized zirconia (YSZ) is a widely recognized ceramic of distinct electrical, mechanical and optical properties. Although YSZ is an intrinsically paramagnetic solid, it could potentially transform to a magnetic semiconductor by incorporating in its crystalline structure isolated atoms bearing unpaired valence electrons. Based on this hypothesis and motivated by the latest advances on YSZ doped with rare-earth atoms, in the current article we report on the electronic and magnetic properties of YSZ doped with Er3+ ([Xe]4f(11)6s(0)) cations that comprise three "unpaired" 4f electrons in their ground state electronic configuration. Our computations, conducted on YSZ 6.7 mol% in Y2O3 doped with two different Er3+ concentrations (3.2 and 6.7 mol% in Er2O3), expose that Er3+:YSZ is a stable antiferromagnetic semiconductor (S=3/2 per Er+3) bearing a rather wide band gap of about 5 eV. All results presented and discussed in current report rely on spin-polarized density functional theory (DFT) within the spin resolved generalized gradient approximation (SGGA) for the pure Perdew, Burke and Ernzerhof exchange-correlation functional (PBE) and hybrid version widely referred as PBE0. According to our knowledge, this is the first time that the magnetic properties of Er3+: YSZ materials are reported for any Er+3 concentration.