Queen Elizabeth II held two virtual audiences on Tuesday, Buckingham Palace said, after she was forced to cancel engagements last week due to Covid.
Concerns have mounted for the 95-year-old monarch's health since she tested positive on February 20, overshadowing the start of her record-breaking 70th year on the throne.
But a palace statement indicated she was now well enough to hold engagements, hosting the new ambassadors of Andorra and Chad from her home at Windsor Castle.
The Queen last week cancelled similar scheduled engagements with new ambassadors as she was suffering from what were described as "mild" Covid symptoms.
A diplomatic reception she was also due to attend on Wednesday this week was cancelled on the advice of Foreign Secretary Liz Truss, due to Russia's invasion of Ukraine.
Buckingham Palace has said it will not give a running commentary on the head of state's health, but confirmation she is undertaking duties again will be seen as a positive.
She was forced to slow down on medical advice after spending a night in hospital following unspecified tests in October last year.
She has rarely been seen in public since.
The Queen became the first monarch in British history to reign for 70 years on February 6, and public celebrations are planned to mark the event in early June.
Senior members of the royal family are due to visit eight of the 14 Commonwealth countries outside the UK where she is also queen and head of state in the coming weeks.
Her grandson Prince William and his wife Catherine are due to tour Belize, Jamaica and The Bahamas in a visit likely to be keenly watched for republican sentiment.
Barbados became the world's newest republic in November last year, ending its three centuries of association with the UK and the queen as head of state.
Both main political parties in Jamaica back the idea of becoming a republic, and could be spurred into emulating their Caribbean counterparts, royal experts say.
The Platinum Jubilee year has also been overshadowed by the Queen's second son, Prince Andrew, who settled a US civil case for sexual assault.
Her eldest son and heir, Prince Charles, is meanwhile under scrutiny after police in London announced a probe into "cash for honours" claims connected to one his charities.