Methane (CH₄) is widely present in groundwater. Dissolved CH₄ in groundwater is less understood when compared with that in wetlands. In this study, the concentrations and origin of dissolved CH₄ in groundwater were investigated and the potential importance of groundwater CH₄ emissions in arid and semi-arid regions of Inner Mongolia was discussed. Groundwater was extracted from domestic wells using a submersible pump or manual power and was analyzed for CH₄ concentrations, δ¹³C-CH₄, and physico-chemical variables. The results show that the concentrations of dissolved CH₄ in groundwater had large spatial variability, ranging from 0 to 0.10 mg L⁻¹ with a mean of 0.01 mg L⁻¹ in Xilingol and from 0 to 8.99 mg L⁻¹ with a mean of 1.44 mg L⁻¹ in Xingan-Tongliao. Substantial CH₄ concentrations of about 2.5–5.5 mg L⁻¹ were found in central areas of Xingan-Tongliao in the winter and the summer. The δ¹³C-CH₄of about −85‰ was highly depleted while CH₄ concentration was significantly negatively correlated with SO₄²⁻ concentration, indicating that dissolved CH₄ in groundwater was microbial in origin. This study suggests that groundwater as a source of CH₄ might have great implications in arid and semi-arid regions worldwide and should deserve more research.