The 12 people were found guilty of taking part in demonstrations and campaigning for the banned opposition group, according to the official. They were distributing leaflets containing religious slogans, something that is not legal in Egyptian campaigns.
They were arrested as part of a crackdown against the banned opposition group. At least 1,000 supporters of the Muslim Brotherhood have been detained in the past two months, and more than a dozen candidates have been disqualified from running in Sunday’s election.
The ban on religious slogans is thought to have been aimed at the Brotherhood, whose motto is "Islam is the solution", and which controls a fifth of Egypt's outgoing parliament.
Observers have seen quotes from the Koran used on posters by other candidates, including some from the ruling National Democratic Party.
Sunday's vote is expected to deliver a victory for President Hosni Mubarak's ruling party and further weaken the Muslim Brotherhood, which has 130 candidates running for the 508 seats left in the race.
The government has pledged the vote will be fair, but rights groups say it has already been compromised by arrests of opposition supporters and restrictions on their candidates.