The statement detailed nearly $3 million in personnel compensation and benefits, more than $800,000 on rent, communications, and utilities, and nearly $532,000 on travel and transportation.
Mueller is heading the investigation into the allegations that Russia interfered in the 2016 US presidential election and claims that Moscow colluded with President Donald Trump's campaign team to affect the outcome of the vote. Similar probes are being carried out in the Senate and the House of Representatives.
Trump has also denied any collusion between himself and the Kremlin, calling Mueller's investigation a witch hunt. The US president said earlier that the Mueller's investigation was based on fraud and should not have been launched.