There was no word of any injuries.
"I do not exclude that this was a terrorist act," Interior Minister Khumdin Sharipov told reporters at the scene on Monday. "This is already the second explosion right on the same place."
In late January, a powerful blast, believed to be a car bomb, rocked the same building in the centre of the Tajik capital Dushanbe, killing a man.
Sharipov said that this time the explosive device was planted on a wheelbarrow of the sort often used by bazaar traders.
Two cars parked nearby were damaged by the blast. Several windows of the Emergencies Ministry were destroyed.
Tajikistan, a Muslim nation of seven million, remains volatile and flooded with weapons after a 1992-97 civil war between Muslim rebels and the secular government which
claimed more than 100,000 lives.