Mr Biden, who is the nation’s oldest serving president at 80, was seen being helped up by Air Force officials and walking back to his seat unassisted.
The president had been standing for about an hour and half to shake hands with each of the 921 graduating cadets.
The White House communications director said “he’s fine”.
“There was a sandbag on stage while he was shaking hands,” Ben LaBolt wrote on Twitter.
A White House press pool report also earlier said Mr Biden had tripped on a black sandbag while moving on stage.
Footage of the incident shows Mr Biden appearing to point at the sandbag as he gets back on his feet.
He was seen jogging back to his motorcade, apparently uninjured, when the ceremony ended shortly after the accident.
Critics have said he is too old to run for a second term as president.
Recent polls have suggested a majority of US voters are concerned about his advanced age. He would be 82 at the start of a second term if he wins.
This fall, in addition to previous stumbles off his bicycle and on the way up the Air Force One stairs, may add to concerns.
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