All the explosives, which authorities had said was enough to flatten a large building, were recovered.
There was no evidence to suggest a link to terrorism, though officials were investigating why the materials had been stolen from the Cherry Engineering's storage depot eight miles southwest of New Mexico's largest city, said Wayne Dixie of the U.S. Bureau of Alcohol, Tobacco, Firearms and Explosives.
A tip led to the arrests, but authorities gave few details.
The brothers, Leslie Brown, 44, of Ignacio, Colo., and David Brown, 49, of Bloomfield, face federal charges including possession of stolen explosives and felons in possession of stolen explosives, Dixie said.
Federal authorities refused to release the names of the other two people who were arrested in Bloomfield. Another person was wanted in connection with the theft.
The explosives included 150 pounds of C-4, 250 pounds of sheet explosives, 20,000 feet of detonator cord and 2,500 blasting caps.
The explosives were intact and it did not appear that anyone had tried to use them, authorities said. Tom McClenaghan, special agent in charge of the Albuquerque FBI, said the brothers did not have experience to use such explosives.