The firing occurred near the frontier in Burundi's western district of Gatumba, a military spokesman said. No one was hurt.
"Congolese soldiers fired on Monday...in the direction of the Burundi frontier post of Gatumba," Burundi army spokesman Adolphe Manirakiza told Reuters.
"It was sporadic shots from machine guns coming from the localities of Kavimvira and Kahorohoro," in the eastern part of Congo, he said.
The Burundian military has asked Congo to clarify the incident, he said.
General Felix Mbuza Mabe, Congo's regional army commander in Bukavu, said the shooting was not directed at Burundian troops.