Mueller met with Senate intelligence chairman Richard Burr and Sen. Mark Warner, the top Democrat on the committee, in a secure room.
Burr told CNN they had a "good meeting" with Mueller.
Burr and Warner have been pressing for the meeting with Mueller since he was first appointed a month ago. The two sides have been discussing "deconfliction" -- or how the Senate investigation and the federal probe will share information and not step on each others' toes.
A major test on that front will be whether the FBI is willing to release memos from former FBI Director James Comey of his conversations with President Donald Trump, now that they have been provided to Mueller.
Asked about the Comey memo, Burr said the committee got "clarity" on whether it can obtain the document, but he would not say whether that means the committee will receive it.
Burr also said he didn't think they would meet in person with Mueller again, but would be in touch if deconfliction issues arise.
"I don't think it's necessary for us to meet (again)," Burr said. "I think we'll be in communication personally with him on any aspects that might bleed over from one to the other."
Director of National Intelligence Dan Coats will meet with members of the committee Thursday, one week after his tense grilling by the panel.
A committee source confirmed Wednesday that Coats would testify in a closed session.
Coats' appearance comes after he promised to answer questions about whether Trump pressured him to rebut stories about the focus of the federal Russia probe. Coats largely declined to answer those questions in a public hearing last week, but he said he would say more in a closed session if he received clearance from the White House.
National Security Agency Director Mike Rogers was on the Hill Monday for a similar closed-door briefing with Senate Russia investigators on whether he was pressured by Trump.