Gates announced in a tweet that he was experiencing mild symptoms.
The billionaire philanthropist said he will isolate until he is healthy again.
"I’m fortunate to be vaccinated and boosted and have access to testing and great medical care," Gates wrote.
The Seattle-based Bill and Melinda Gates Foundation is the most influential private foundation in the world, with an endowment of about $65 billion.
Bill Gates has been a vocal proponent for pandemic mitigation measures, specifically access to vaccines and medication for poorer countries.
In January, the foundation reportedly donated $1.75 billion to fighting the pandemic and developing COVID-19 vaccines.
Just before Christmas, Gates had announced that he had largely scrapped his holiday plans due to the latest COVID-19 variant, omicron, citing concerns over its rapid spread.
At that time Gates said in a tweet, "Just when it seemed like life would return to normal, we could be entering the worst part of the pandemic."
The Gates Foundation in October said it will spend $120 million to boost access to generic versions of drug maker Merck’s antiviral COVID-19 pill for lower-income countries.