The FBI said Tuesday there was no danger to the public because the explosive devices were inoperable and were controlled by an undercover FBI employee.
Three men were arrested Monday on charges of conspiracy and trying to use explosive to damage property affecting interstate commerce. Charges were pending against two men.
The suspects range in age from 20 and 35. Authorities say at least three are self-described anarchists and are not tied to international terrorism.
The FBI says the target of the plot was a bridge over the Cuyahoga (keye-uh-HOH'-gah) Valley National Park in the Brecksville area, roughly 15 miles south of downtown Cleveland.
Associated Press writer Pete Yost in Washington contributed to this report.