We present the results of theoretical calculations of the electronic structure of the Sb/GaAs(110) interface in the submonolayer coverage regime performed in the full ab initio self-consistent pseudopotential scheme. Different structural models for the edges of the extended Sb islands have been considered and their equilibrium geometry has been determined by total energy minimization. The single particle band structure shows interface states arising mainly from the incomplete bonding of the Sb adatoms at the terrace edge to the substrate, which fall within the optical gap. Distinct features are associated to different island terminations. The interface turns out to be metallic in all the considered cases with a partially occupied peak at the Fermi level. We have also studied the effect of including explicitly the on-site Hubbard electron-electron correlation in the calculation of the quasiparticle spectrum, obtaining the observed semiconducting interface when the Coulomb interaction parameter U is larger than 3 eV. The interface states within the optical band gap can be present also at higher coverages when some disorder exists, evidentiating a general mechanism for the Fermi level pinning at this interface.