We present our study on the adsorption of C, Si and Ge adatoms on binary compound germanium carbide (GeC) honeycomb structure based on density functional theory using the generalized gradient approximation. We found that C atom is bound at bridge site, while Si and Ge prefer to adsorb to top site above the top of carbon. The electronic and magnetic properties of GeC can be modified by the adsorption of these adatoms. Nonmagnetic semiconductor GeC is either metal or narrow band gap semiconductor depending on the adatoms coverage. One of the reason of this effect is the bonding combination of adatom-p and GeC-sp(2) orbitals. All the adatom adsorptions on GeC have zero net magnetic moment, except Ge adsorption at low coverage, which has a net magnetic moment of mu = 2.0 mu(B) per cell. Our results also indicate that because of the charge transfer, the adsorption of C and Si/Ge on a GeC surface allow us to obtain p- and n-type doping, respectively. Therefore, adatom covered GeC can serve as an interesting alternative for the nanodevice applications. (C) 2015 Elsevier B.V. All rights reserved.