We investigate the standard model (SM) with a U(1)B-L gauge extension where a B-L charged scalar is a viable dark matter (DM) candidate. The dominant annihilation process, for the DM particle is through the B-L symmetry breaking scalar to a right-handed neutrino pair. We exploit the effect of decay and inverse decay of the right-handed neutrino in thermal relic abundance of the DM. Depending on the values of the decay rate, the DM relic density can be significantly different from what is obtained in the standard calculation assuming the right-handed neutrino is in thermal equilibrium and there appear different regions of the parameter space satisfying the observed DM relic density. For a DM mass less than O(TeV), the direct detection experiments impose a competitive bound on the mass of the U(1)B-L gauge boson Z′ with the collider experiments. Utilizing the nonobservation of the displaced vertices arising from the right-handed neutrino decays, the bound on the mass of Z′ has been obtained at present and higher luminosities at the LHC with 14 TeV center of mass energy where an integrated luminosity of 100 fb-1 is sufficient to probe mZ′∼5.5 TeV. © 2018 authors. Published by the American Physical Society.