Due to limitations of the Standard Model of particle physics, several extensions like Grand Unification Theories, supersymmetric and extra-dimensional models have proposed. Several such models with extended gauge groups often feature additional symmetries with corresponding heavy Z’ bosons. The decay of these heavy particles would manifest itself as a narrow resonance on the dilepton or dijet mass spectrum. This talk presents searches for such narrow resonances on the dilepton and top-antitop mass spectrum with the ATLAS detector. The dilepton search results are shown using partial Run-2 proton-proton collision dataset of 36 fb$^{-1}$ at $\sqrt{s} = 13$ TeV. The top-anitop resonance search results, one the other hand, uses the full Run-2 proton-proton collision dataset of 139 fb$^{-1}$. The talk further summarizes several limitations related to top-antitop resonance search and particularly discusses one issue related to tracking in the dense environment where pixel charge deposits merge in the ATLAS inner detector. The talk highlights that Mixture Density Network-based algorithm performs better in splitting the merged pixel charge clusters and could be a potential algorithm for Run-3.