Asked if the prime minister's premiership was over if it could be proved that he had lied to parliament, Raab said: "Look, the suggestion that he's lied is nonsense.
"He's made it very clear to the House of Commons, took questions on this, that he thought it was a work event," he told Times Radio.
Johnson last week apologised to parliament for attending a "bring your own booze" gathering in the garden of Downing Street on May 20, 2020, but said he had thought it was a work event.
Dominic Cummings, an architect of Britain's departure from the European Union and a former senior adviser to Johnson who left government under acrimonious terms in November 2020, said that Johnson had agreed that the drinks party should go ahead.
"Not only me but other eyewitnesses who discussed this at the time would swear under oath this is what happened," he said on his blog.