Trump campaign communications director Tim Murtaugh told ABC News quarantine procedures were immediately implemented.
"No COVID-positive staffers or anyone in immediate contact will be at today's rally or near attendees and elected officials," Murtaugh said in a statement.
Two Secret Service agents are among the six advance staff in Tulsa that have tested positive for COVID-19, a source familiar with the matter tells ABC News.
Tulsa has seen cases of COVID-19 spike in the past week, and the local health department director asked that the rally be postponed. But Republican Gov. Kevin Stitt said it would be safe. The Oklahoma Supreme Court on Friday denied a request that everyone attending the indoor rally wear a mask, and few in the crowd outside Saturday were wearing them.
The Trump campaign said it will hand out masks and hand sanitizer, but there is no requirement that participants use them. Participants will also undergo a temperature check.
The Associated Press contributed to this report.