Reduced graphene oxide (rGO) is a potential candidate for hydrogen storage technologies as it shows a high reactivity to hydrogen. Here, we study how muon behaves in rGO (Graphenea) that is thermally modified at 200°C, particularly compared to that as prepared one. The investigation is performed by means of muon-spin relaxation (μ+SR) technique which is sensitive to hydrogen reaction in low electron-density materials like rGO. At 300 K, a considerable fraction of captured muoniums is observed in the thermally modified rGO (~38%), which is slightly higher than that of as prepared rGO (~35%). These appreciable fractions indicate a vigorous interaction between rGO and hydrogen, suggesting the potential of rGO for hydrogen storage. Moreover, the fraction of muon diffusion in rGO subtly decreases, while the fraction of muon experiences local dipolar interaction with nearby proton somewhat increases by thermal modification at 200°C. A subtle alteration in the muon diffusion fraction is expected due to an increase in the number of defects presented in thermally modified rGO.