The agency said that the lab in question failed to follow correct procedures to inactivate samples of live Bacillus anthracis, also known as anthrax.
The samples were then moved by workers, thinking that the samples had been deactivated, who did not wear the proper protective equipment.
The CDC said in a statement that it had taken "aggressive steps to protect the health of all involved," though the potentially exposed staff have a "very low" risk of infection.
"The general public are not at risk of exposure and do not need to take any protective action," the agency said.
They've been given antibiotics as a precaution.
An investigation is under way to determine why staff did not follow proper procedures.