These are the fourth general elections since independence in 1990
Campaigning in Namibia has been hit by legal rows ahead of polls on Friday.
The National Society for Human Rights is going to court after the electoral commission withdrew its observer status, saying it was not impartial.
Meanwhile, a party that has split from the ruling Swapo party has told the BBC its leader is being sued for $13m after saying previous polls were rigged.
Swapo candidate President Hifikepunye Pohamba is seeking a second term after winning a landslide victory in 2004.
Hidipo Hamutenya, leader of the Rally for Democracy and Progress (RDP) which broke away from Swapo in 2007, is seen as Mr Pohamba's main rival for the presidency in the two-day election.
The BBC's Frauke Jensen in the capital Windhoek says the National Society for Human Rights (NSHR) has been extremely vocal in its criticism of the electoral commission.
It says the voters' roll includes constituencies that have been listed twice, voters who have been listed twice and under-age people - a discrepancy of about 180,000 voters. The Electoral Commission of Namibia has rejected the allegations.
On Wednesday evening, RDP spokesman Libolly Haufiku confirmed to the BBC that Mr Hamutenya was being sued for $100m Namibian dollars ($13m; £8m) by Swapo for his comments made during the campaign.
Mr Haufiku said he could not comment further as the case was before the courts.
NAMIBIA GENERAL ELECTIONS
Presidential and parliamentary ballots
12 presidential candidates
72 seats in parliament
1.1m registered voters
Voting on Friday and Saturday
Our correspondent says that the case has not been reported in the local media.
A former colleague of Mr Pohamba, Mr Hamutenya served as trade and foreign minister in previous Swapo governments.
Amid the political tussles, the president has made a public appeal for calm.
"I wish to make a heartfelt appeal to all registered voters and the Namibian people in general to conduct themselves in a peaceful and tolerant manner," President Pohamba said on state television on Wednesday night.
Some 1.1m registered voters are eligible to cast their ballots on Friday and Saturday for a president and members of the National Assembly.
Swapo has dominated Namibia's politics since it gained independence in 1990 after a long struggle against rule by South Africa.