The Maine Republican added that if any audio recordings do exist, she expected Trump to provide them to federal investigators looking into Russia's efforts to influence the 2016 election, saying if he did not, he should be legally compelled to do so.
"He should give a straight yes or no," Collins told anchor Brianna Keilar. "And he should voluntarily turn them over. ... I don't understand why the President just doesn't clear this matter up once and for all."
Comey was leading the FBI's investigation into Russian meddling in the US election when Trump fired him last month.
Collins also said she thought Department of Justice special counsel Robert Mueller, who now leads the Russia probe, would be more likely than Congress to compel the release of any audio recordings.
"I would be fine with issuing a subpoena," Collins said. "But that most likely would come from the special counsel's office."
Shortly after firing Comey, Trump issued a vague threat on Twitter, saying Comey had "better hope that there are no 'tapes' of our conversations before he starts leaking to the press!"
The White House has refused to confirm or deny the existence of any tapes or recordings, and Trump hinted at a press conference in the Rose Garden on Friday that there actually aren't any recordings of his meetings and phone calls with Comey.
Jay Sekulow, a member of President Trump's private legal team, said Sunday on ABC News' "This Week" that Trump will address the existence of any recordings in the coming week.
The President also said at the Friday press conference that he would deny under oath Comey's claim that he privately asked him to back off his investigation into former national security adviser Michael Flynn.
"I didn't say that," Trump said of the claim about Flynn, who resigned in February after it emerged that he misled
Vice President Mike Pence about phone calls he held with Russian ambassador Sergey Kislyak during the transition.
Asked if he would testify under oath to Mueller to that effect, Trump replied: "100 percent," adding, "I would be glad to tell him exactly what I just told you."
For his part, Comey told
the Senate intelligence committee in testimony Thursday
, "Lordy, I hope there are tapes" because they would back his side off the story, which Trump has challenged.
Trump attacked Comey again on Twitter on Sunday morning, calling Comey a coward and suggesting his decision pass his recollection of private conversations with Trump to the press could be illegal.
Comey's word vs. Trump's
Trump and his lawyer, Marc Kasowitz, have denied Comey is telling the truth about his one-on-one conversations with Trump.
Collins said she believed Comey did tell the truth in his testimony, in which he recounted his conversation with Trump about Flynn, but she also allowed for the possibility "there was a misinterpretation." Regardless, she said, Trump was "certainly wrong" to say what Comey said he had about the Flynn investigation.
Collins said she believed Trump simply did not know how to behave and was unaware of the independence that an FBI director should be afforded. She said someone, either in the White House, the administration or Comey himself, should have set Trump straight.
"The President clearly does not fully understand or appreciate the boundaries," Collins said. "But he should. I'm not excusing his behavior."