McConnell was speaking during the confirmation proceedings Thursday for Elena Kagan to the U.S. Supreme Court when Franken allegedly gesticulated and made faces while presiding, The Hill reported.
Television cameras broadcasting the floor session were directed on McConnell as he delivered his statement of opposition to Kagan, missing Franken's actions that witnesses reported seeing.
After McConnell finished his remarks, he walked to the chair to chastise Franken, telling Minnesota's junior senator, "This is not 'Saturday Night Live,'" referring to Franken's career as a writer and actor on NBC's long-running late-night comedy show, a witness overhearing the exchange told The Hill.
After the vote, Franken went to McConnell's office to apologize, aides said.
"The leader thought I was disrespectful while he was giving his speech on (Kagan)," Franken said in a statement to The Hill. "He is entitled to give his speech with the presiding officer just listening respectfully. I went directly to his office after I was done presiding to apologize in person. He wasn't there, so I've sent him a handwritten note."