The Kosovo Foundation for Open Society told InSerbia.info it had received more than 1,500 reports of potential problems by noon Sunday, although voting appeared to be proceeding peacefully.
Kosovo residents were choosing local representatives for the first time since 1999.
Kosovo has been a source of friction between its ethnic Albanian and Serb residents over the possibility of independence from Serbia.
The stakes in the election also include its impact on Serbia's bid to join the European Union. The EU has insisted on a clean election in Kosovo as a condition for Serbia's membership.
InSerbia.info said turnout among Serbs in the northern reaches of the province was worrisome to some provincial officials, who warned a boycott could lead to an outcome the Serbs who refused to vote would not be pleased with.