The BBC reported a largely peaceful balloting process and the European Union said it was encouraged by the turnout.
EU observer Thijs Berman said it was unclear how extensive the alleged irregularities were.
"We are busy evaluating this," he said.
The Ethiopian People's Revolutionary Democratic Front was expected to remain in power despite allegations the party intimidated voters and restricted media coverage leading up to the vote.
"Behind an orderly façade, the government pressured, intimidated and threatened Ethiopian voters," said Rona Peligal, acting Africa director at Human Rights Watch. "Whatever the results, the most salient feature of this election was the months of repression preceding it."
The election was the first national parliamentary election in Ethiopia since the violent suppression that followed the 2005 polling that nearly saw Zenawi's party ousted. Nearly 200 people died in the violence.