The ministry said the incident occurred at around 7:45 a.m., Romanian time.
Captain Iuliu-Vasile Unguras, 32, was leading a patrol mission formed of four Humvees on the A1 highway linking Kandahar to Kabul. One of the vehicles ran over an improvised explosive device 20 kilometers north-east of Qalat and Unguras died, while another four militaries were injured.
The casualties were taken to military hospitals in Lagman and Kandahar.
Captain Unguras, the third Romanian to be killed in Afghanistan this year, was married and had two children.
Another Romanian officer was killed Friday morning in Afghanistan, about 80 kilometers south-west of Kabul, while fighting insurgents alongside a U.S. mission. He was 33, married, with a child.
Eleven Romanians were killed in Afghanistan since 2003, when Romania started participating to NATO missions in the country.
Romania currently has 956 troops in Afghanistan, according to the Defense Ministry.