Wearing a mask, the president waved inside a car moments after tweeting that he would pay a "surprise visit".
Mr Trump, who has been criticised for his handling of the pandemic, also said he had learned a lot about the virus.
Earlier, his doctors said Mr Trump continued to improve and might be discharged as early as Monday.
Dr Sean Conley said the president's oxygen level dropped twice since his diagnosis, and he was started on a steroid called dexamethasone.
The president was given extra oxygen at least once after testing positive, said Dr Conley, who also sought to clarify earlier confusion caused by conflicting statements about Mr Trump's condition.
In a tweet, the president - dressed in a suit jacket and shirt with no tie - said: "I learned a lot about Covid. I learned it by really going to school. This is the real school. This isn't the let's read the books school. I get it and I understand it. It's a very interesting thing, I'll be letting you know about it."
The president's diagnosis, which he made public in a tweet early on Friday, has upended his election campaign. Mr Trump faces Democratic challenger Joe Biden on 3 November.