We report the local top-gated graphene resonator inertial mass sensing of mixed H2/Ar gas. The graphene resonator is fabricated with monolayer graphene. The fabricated resonator dimensions are 900 nm in length and 500 nm in width. Measurements of the fabricated resonator are performed using a co-planar structure probe and radio-frequency (RF) connectors. At the vacuum condition of the chamber, the resonant frequency of the doubly clamped graphene resonator is measured as 94.3 MHz with the quality factor of 42.2, based on transmission S-parameter characterization. The measured resonant frequency is consistent with the theoretical calculation based on the continuum model for the graphene resonator. When the chamber pressure is increased to 1.1×10-1 Pa by injecting mixed H2/Ar gas, the resonant frequency of the device is downshifted by 4.32 MHz to 89.98 MHz and the quality factor is reduced to 22.5. As the mass of the graphene resonator is increased by the adsorption of mixed gas molecules adsorption, the resonant frequency is downshifted further. The detected mass of the adsorbed gas molecules is calculated as ∼15 attograms.