BELGRADE, Yugoslavia, July 29— Six more people in the southern region of Kosovo were sentenced today to prison for counterrevolutionary activity involving ethnic Albanian riots, officials said.

Three workers and two students were sentenced to terms ranging from six and a half to eight and a half years after a two-day trial in Kosovska Mitrovica.

The five were accused of organizing and participating in agitation in March and April that took the lives of at least nine people and injured more than 250.

The sixth defendant, an 18-year-old student, was tried in the provincial capital of Pristina and give six years. Officials said the student wrote anti-Yugoslav poems and pamphlets, distributing them to fellow students. He was also accused of participating in the demonstrations.

Last week, three ethnic Albanians were sentenced at Kosovska Mitrovica to jail terms ranging from six to eight years. About 150 others are awaiting trial in Kosovo, including the alleged ringleaders. More than 2,000 people were arrested after the riots and many spent up to 60 days in prison for minor offenses.