No additional information about the technical problem was immediately available.
Earlier reports indicated the facility, which employs more than 3,000 research and support workers, was placed on lockdown due to the presence of an unidentified gunman. Local police swarmed to the NASA center and its main gates were blocked off from traffic, according to media reports.
But an "all clear" announcement was made shortly before 11 a.m., declaring that "the emergency is over," reports indicated.
NASA's Glenn Research Center sits on a sprawling, 350-acre campus that's almost adjacent to Cleveland's Hopkins International Airport. It boasts more than 140 buildings and is home to 24 major facilities. Officials said that airport operations were not affected by the incident.
Scientists at Glenn focus on research into space exploration and aeronautics. "Our work is focused on technical advancements in spaceflight systems development, aeropropulsion, space propulsion, power systems, nuclear systems, communications and human research," Glenn officials state, in a note on the facility's web site.
"We continue to contribute to economic growth and national security by developing technology for safe, superior, and environmentally compatible U.S. aircraft propulsion systems," according to the Web site.
NASA Glenn has won numerous awards, including 98 "R&D 100" honors, four NASA Software of the Year awards, two Collier trophies, and even an Emmy Award. Scientists at the facility have also claimed more than 2,000 inventions since 1991.