Volodymyr Zelensky (L) and his wife Olena during a presidential election debate in Kiev. Fiel / AFP
Zelenska, 42, added that her husband, President Volodymyr Zelensky, and their two children tested negative.
"Today I've received a positive COVID-19 test result," she said on Facebook.
On Thursday, Ukrainian authorities said there had been an "alarming" rise in coronavirus cases as the country eases lockdown restrictions.
On Friday, the ex-Soviet country reported 29,753 cases and 870 fatalities. The Ukrainian president urged officials to urgently establish the reason behind a spike in new cases.
"Only the observation of security measures will protect us from the threat of getting sick and save our economy from the quarantine," he said.
President Volodymyr Zelensky and Olena Zelenska attend the enthronement ceremony of Japan's Emperor Naruhito in Tokyo. Reuters
The first lady said that she felt fine and was self-isolating. She said the positive test was a surprise as she and her husband have sought to follow social distancing rules and protected themselves.
But the 42-year-old leader came under fire last week when he appeared without a mask in a cafe during a visit to the city of Khmelnytsky in central Ukraine.
Some experts have said the uptick is due to an increase in testing.
Lockdown measures eased gradually in late May and early June with a resumption of public transport, including metro systems and long-distance and local train services.
Ukraine launched domestic flights on June 5 and will resume international flights on Monday.
Elsewhere in Europe, frustrations with COVID-19 curbs were spilling over, with scuffles breaking out at a large anti-restrictions protest in the German city of Kassel, and thousands joining a similar demonstration in Liestal, Switzerland.
England's months-old rules have been relaxed thanks in large part to a successful vaccination drive, enabling outdoor gatherings of up to six people, or two households, in what newspapers have dubbed "Happy Monday."
The global death toll from the virus surged past 106,000 on Saturday, with the United States quickly becoming the epicentre of the pandemic that first emerged in China late last year.
Some intensive care specialists are trying to hire more permanent staff. Others want to create a reservist "army" of medical professionals ready to be deployed wherever needed to work in wards with seriously ill patients.
The Abu Dhabi Police have affirmed that drivers can object to traffic fines within a month from the date an SMS to this effect has been received by the vehicle owner.
CEO Mark Zuckerberg, speaking at the company's live virtual and augmented reality conference, said the new name reflects his focus on building the metaverse.
Besides celebrating reading and culture, the milestone Sharjah International Book Fair 2021 (SIBF), being organised by the Sharjah Book Authority (SBA) at Expo Centre Sharjah from November 3 to 13, has announced 12 workshops focused on social media and online marketing for all age groups.
The National Centre of Meteorology (NCM), through the UAE Research Programme for Rain Enhancement Science (UAEREP), has carried out a research campaign in Colorado, United States of America, to investigate the possibility of using autonomous unmanned aircraft systems to collect cloud microphysical measurements and provide automated cloud seeding decisions.