In this study, we examined the anaerobic incubation of waste-activated sludge (WAS) under thermophilic conditions. First, we reconfirmed CO₂ sequestration using WAS without any enrichment process at different temperatures under mixed gases (CO₂:H₂ = 1:4). We observed that the methanogens, which were previously enriched at 37°C, displayed strong CO₂ sequestration at an early incubation time. Although CO₂ sequestration at 60°C showed the largest impact after 6 days, no methane production was observed at each thermophilic condition within 4 days. Therefore, we enriched methanogens using a novel WAS protocol for 10 days under nitrogen gas under thermophilic conditions. These methanogens displayed better CO₂ sequestration than the original strain at 37°C. Moreover, methane production by the thermophilic methanogens was due to the hydrogenotrophic pathway rather than the acetoclastic one because low methanogenic activity from acetate was observed. Microbial community structure analysis showed that the Methanothermobacter genus belonging to hydrogenotrophic methanogens was predominant among the thermophilic enriched methanogens at 60°C. Taken together, the thermophilic methanogens can be a useful tool to sequestrate CO₂ efficiently.