11:16 AM PT -- Joe Biden just boarded Air Force One -- and he walked out of his SUV with a mask in hand.

Of course, he was peppered with questions by reporters on hand -- who asked how he was feeling, and whether he thought Kamala Harris could beat Donald Trump. He replied with an inaudible answer and then went up the big stairs to get on the airplane. We'll see him in D.C. soon.

President Joe Biden is on the move -- surfacing in public for the first time since his COVID diagnosis ... and based on this video we just got, it looks like he's still playing it safe.

TMZ obtained footage of JB and his presidential motorcade leaving his Rehoboth Beach, DE home Tuesday -- and as you can see, POTUS had a fleet of SUVs driving down the road ... and Joe himself was spotted in the backseat of one of them, rocking a face mask.

Indeed ... you can quickly see Biden through the window, where he looked to be waiving to bystanders -- and from the looks of it, he's in good spirits ... and, reportedly, good health too.

Word is, Biden has tested negative for COVID -- and he's now on his way back to D.C. right now to hit the White House and settle back in before he addresses the nation Wednesday.

We already heard from Joe Monday -- when he beamed into the campaign headquarters in Wilmington, DE to address his staff and reiterate his support for Kamala Harris -- but once JB touches down, we'll get the first full view of him since he left Las Vegas last week.

Upward and onward, as they say.