His Ethiopian People's Revolutionary Democratic Front denies it repressed its opponents and says that candidates are able to campaign freely.
But two opposition members have died under mysterious circumstances during the election campaign.
In 2005, after the opposition won an unprecedented number of parliamentary seats, clashes between police and demonstrators left 193 people dead.
"People are so terrorised they just want this election to be over, and they want to go back to their miserable lives," Berhanu Nega, a former politician, said.
He lives in political exile in the US and has been sentenced to death in absentia in Ethiopia.
|Zenawi's Ethiopian People's Revolutionary Front has been in power since 1991 [AFP]
The country is frequently criticised for its human-rights record, including by the US, which issued a report this year citing "unlawful killings, torture, beating, abuse and mistreatment of detainees and opposition supporters by security forces, often acting with evident impunity."
However, the US considers Ethiopia an ally in the region against what is seen as Islamic extremism in neighbouring Somalia.
Ethiopia is reliant on billions of dollars of foreign aid, most of it from the US, and oppositions parties claim that this is also being used to garner votes for the ruling party.
Gus Selassie, a London-based analyst with IHS Global Insight, said that there was "a marked sense of fear and trepidation surrounding the build-up" to the elections.
The government said that observers from the European Union and the African Union could monitor the vote along with 40,000 local observers.