"This unfortunate incident happened after a hostile mortar round had fallen near the camp they were staying," the 10-nation Southern African Development Community (SADC) said in a statement.
It gave no further details about the incident.
A soldier from South Africa has also died in hospital while being treated for health problems, it added.
The regional bloc deployed 2,900 soldiers to North Kivu province in December to help DRC government forces battling M23 rebels.
After several years of dormancy, the M23 (March 23 Movement) took up arms again in late 2021 and has seized vast swathes of the province.
Western governments and the United Nations have accused neighboring Rwanda of backing the Tutsi-led M23, allegations Kigali denies.
The Southern Africa force includes soldiers from regional military heavyweight South Africa, Tanzania and Malawi.
The force suffered its first losses in mid-February when two South African soldiers were killed by mortars.