Burr had said Monday that Stein's campaign was one of two that the committee was beginning to investigate.
"I think it's safe to say we have two other campaigns we are just starting on," the North Carolina Republican said when asked whether the panel had interviewed a majority of the witnesses in the Russia probe.
Asked what his panel wanted to learn from the Stein campaign, Burr said whether there was "collusion with the Russians."
The senator did not identify the second campaign he was referring to on Monday, and a spokeswoman declined to comment.
On Tuesday, Burr was asked to clarify the second campaign he was referring to, and he confirmed it was not the Bernie Sanders campaign, since he was referring to campaigns in the general election.
"How many campaigns were there in the general election? ... Bernie Sanders wasn't in the general election," Burr said.
The senator added: "I said at the beginning we would look at all the campaigns and possible collusion by any campaign."
Sanders, the Vermont independent who lost the Democratic presidential nomination to Clinton last year, told CNN on Tuesday that "to the best of my knowledge" no one on the Intelligence Committee had reached out to him or his associates. The 2016 Libertarian candidate, Gary Johnson, told CNN on Tuesday that he and his advisers had not been contacted by the panel and had had no communication with any Russian officials.
The revelation that Johnson and Sanders have not been contacted by the panel suggests that Burr still wants to question Clinton witnesses as part of the investigation.
The committee has already spoken to numerous officials from the Donald Trump and Clinton campaigns as part of its investigation into Russian election meddling and possible collusion.
Stein is of interest to the congressional Russia investigators in part because she attended the same gala for Russian state television broadcaster RT in 2015 that former Trump national security adviser Michael Flynn attended.
Photos and video have shown that Stein was seated at the same table as Flynn and Russian President Vladimir Putin.
On Tuesday, Sen. Mark Warner, the Virginia Democrat who's the vice chairman of the committee, declined to say if Stein was indeed a new focus of the probe. But he said: "I will point out that Miss Stein did attend that infamous dinner with Gen. Flynn that did include Vladimir Putin, and we have seen reports that Stein ... [was] very complimentary of Julian Assange and WikiLeaks, which we know was one of the pawns being used by the Russians, so I think there are questions, but again I'm not going to confirm who we're looking at and not looking at."
Warner also declined to discuss what other campaigns the panel wanted to investigate.
In an interview with CNN's Michael Smerconish earlier this year, Stein said her trip to Moscow for the RT dinner was part of a "peace offensive in the Middle East" and that the trip did not boost her profile in the US.
"That picture actually didn't begin to circulate until long after the election," Stein said. "So it's not like it was a public relations bump. It essentially wasn't covered here in the US. There was media at that conference, and it was a daylong conference, where my message was very clear. ... This was not a message that was particularly friendly to the Russians. It was saying to them that we need to stop the bombing" in Syria.
In a statement Monday night, Stein denied any wrongdoing.
"Our campaign has observed the highest standards of transparency and integrity in our interactions with foreign nationals as well as Americans," Stein said in a statement.