Who was in charge of investigating claims of communist activity in the government

House Un-American Activities Committee

Explanation:

House Un-American Activities Committee was formed in 1938 to investigate the subversive activities and disloyalty of the organisations, public employees and private citizens suspected of having ties with the communists. It was also known as House Committee on Internal Security.

The committee was abolished in 1975 and its functions were given to the House Judiciary committee. Its investigations are compared often compared with those of Joseph McCarthy but he didn't have any involvement with this committee.