"There has been no obstruction. There has been no collusion. There has been leaking by Comey. But there's been no collusion, no obstruction, and virtually everybody agrees to that. So we'll have to see," Trump told the broadcaster in an interview, an excerpt of which was released late Thursday.
On June 8, Comey acknowledged in a congressional testimony that Trump had not directed him to end the investigation.
The US president also questioned the independence of Mueller's investigation as it included people who supported then Democrat presidential nominee Hillary Clinton.
"I can say that the people that have been hired are all Hillary Clinton supporters," Trump said.
Obstruction of justice is a criminal offense in the United States, and such charges were included in the articles of impeachment for former presidents Richard Nixon and Bill Clinton.
Since the beginning of the United States' last presidential race, US media have speculated about Trump's campaign team's alleged ties to Russia and claimed that Moscow might have influenced the results of the election.
In January, the US intelligence community presented a report on Russian activities, expressing, with a high degree of confidence, that Russia's goal was to influence the election so that Trump could win.
Russian officials have repeatedly denied charges of interfering in the US elections, saying the allegations are absurd and represent an attempt to divert the US public’s attention other pressing domestic issues.
