The detentions took place in five provinces. A senior Brotherhood official, Ali Abd al-Fattah, said the detainees had been playing an active role in the outlawed group's election campaign.
"The police are back to their old habits of cracking down on the Brotherhood," Abd al-Fattah said.
The group's media coordinator, Abd al-Munaim Muhammad, said the police had detained members in three Nile Delta provinces, the port city of Alexandria, the southern Qina province, and in Fayum - a town south of Cairo.
A police official confirmed the arrest of 143 people in various provinces. The official spoke on condition of anonymity as he was not authorised to speak to the press.
Around 50 were detained in Alexandria according to security sources who said the people were detained at their homes or on their way to polling stations to prevent them from rioting or causing violence.
The statement said that while carrying out the arrests, the security forces confiscated "sticks, light weapons, Molotov cocktails, metal chains and Egyptian and foreign currency".
Violence have marred Egypt's
The arrests on Friday coincided with controversy over an investigation conducted by judges supervising the elections, which found that officially announced results in the Nile Delta city of Damanhur differed from their own vote count.
The discrepancy was discovered after Damanhur's Muslim Brotherhood candidate, who lost to a candidate of the ruling National Democratic Party (NDP) lodged a complaint.
The Brotherhood spokesman said the arrests in Alexandria were an attempt by the NDP to hamper their election campaign, after the Brotherhood won seven seats in the city in the first round of the second stage of elections.
The NDP gained only two seats.
"This is a warning from the authorities and an attempt to cut off the Brotherhood leadership from their supporters. It is also a punishment for winning seven seats," Brotherhood spokesman Abd al-Munaim Mahmud said.
The elections are spread over six days of voting - two rounds for each of the three stages. The second round of the second stage begins on Saturday.
A judge supervising the elections said Damanhur's officially announced vote count, which gave victory to NDP candidate Mustafa al-Fiqi, did not correspond with the number of votes they counted.
Judge Ahmad Miki, head of the Election Observation and Evaluation Committee, said that newspaper reports that al-Fiqi gained only 8606 votes against Brotherhood candidate Jamal Hishmat's 24,611 votes were correct.
"This is a warning from the authorities and an attempt to cut off the Brotherhood leadership from their supporters"
Abd al-Munaim Mahmud, Brotherhood spokesman
Alexandria is a Brotherhood stronghold, and has been a flashpoint for election violence.
Nearly 540 Brotherhood supporters have been arrested since the beginning of the parliamentary elections earlier this month, and about 300 still remain in prison, a Brotherhood source said.
The Brotherhood has so far won more than 40 seats, making it the largest opposition group, and its results are a significant improvement on its showing in the 2000 elections when it won just 17 seats.
Candidates in the current run-off are contesting 121 seats out of a total of 166 in the second phase. There are 444 elected seats in the People's Assembly as a whole.
The third and final phase is due to be held on 1 and 7 December and Parliament is scheduled to begin its new session on 13 December.