The building has been closed since April 29 when the worker was found to have the flulike illness known as severe acute respiratory syndrome, according to the wire agency AFP.
The building houses 1,000 staff members, who are now working from home or at Motorola's other offices in west Beijing, according to a Motorola representative quoted in the report.
The infected staff member, a manager, is said to be recovering.
The Chinese capital is gripped with fear over SARS, which has infected more than 6,700 people worldwide and caused nearly 480 deaths since last fall, according to the World Health Organization.
China, where SARS is believed to have originated, is the hardest-hit country. China and Hong Kong account for more than 6,050 of the infections and more than 400 of the deaths, according to the WHO.
In late March,from the production line after one of them became ill with SARS. The quarantine period has since ended.
Motorola, which is based in Schaumburg, Ill., is China's leading mobile-phone maker by market share, but global rivals such as Nokia and lower-priced domestic brands are catching up quickly.
CNETAsia staff reported from Singapore.