The NIH said in a statement that Fauci will isolate and continue to work from home. He has not been in close contact with President Joe Biden or other senior government officials.
Fauci is fully vaccinated and has received two booster shots, the health agency said.
The 81-year-old is the director of the National Institute of Allergy and Infectious Diseases (NIAID), and is part of the NIH, and chief medical advisor to the president. He was a leading member of the White House coronavirus task force under former President Donald Trump.
According to the NIH, Fauci will follow virus guidelines from the Centers for Disease Control and Prevention (CDC) and advice from his doctor, and will return to the work when he tests negative.
Earlier this week, U.S. Health Secretary Xavier Becerra tested positive for the virus. It was the second time Becerra had come down with symptoms and tested positive.
The Associated Press contributed to this story. This story was reported from Washington, D.C.