"A contractor based in our Stadium East office has been diagnosed with the COVID-19," a spokeswoman said in an emailed statement.
Facebook said it has notified employees, adding that workers in all Seattle locations were being encouraged to work from home until the end of the month.
Seattle in Washington state has the largest concentration of coronavirus cases confirmed to date in the United States.
Online retailer Amazon.com Inc on Tuesday reported the first case of the virus among its US employees.
The news of the Facebook contractor being diagnosed with the coronavirus was first reported by Bloomberg.