The effect of annealing under argon atmosphere on hydrogenated amorphous silicon (a-Si:H) thin films deposited at room temperature and $300^{circ}C$ using Radio Frequency (RF) magnetron sputtering has been investigated. For the films deposited at room temperature, there was not any increase in hydrogen content and optical band gap of the films, and as a result, quality of the films was not improved under any annealing conditions. For the films deposited at $300^{circ}C$, on the other hand, significant increases in hydrogen content and optical band gap were observed, whereas values of microstructure parameter and dark conductivity were decreased upon annealing below $300^{circ}C$. In this study, it was proposed that the Si-HX bonding strength is closely related to deposition temperature. Also, the improvement in optical, electrical and structural properties of the films deposited at $300^{circ}C$ was originated from thermally activated hydrogen bubbles, which were initially trapped at microvoids in the films.