The leaders, including BNP chairperson Khaleda Zia's adviser Khandaker Mahbub Hossain, were arrested in a sudden crackdown in the capital.
Two former lawmakers, Fazlul Haque Milon and Nazimuddin Ahmed, were arrested during a raid on the office of BNP chief whip Zainul Abdin Farroque.
Four more opposition activists were detained from various parts of Dhaka, but were released later. Party chief Zia has been confined to her home for the past two weeks.
The fresh arrests came a day after Hasina ordered army and law enforcement agencies to restore peace and order at any cost, saying restoring peace would be the first task of her new government.
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The fresh shutdown, alongside an ongoing indefinite blockade of railways, roads and waterways, has brought the entire country to a grinding halt.
Sunday's general election was boycotted by the 18-party opposition alliance led by the BNP. Premier Sheikh Hasina's Awami League secured over a three-fourth majority in the polls marred by deadly clashes and a low turnout.
The BNP boycotted the polls after Hasina rejected the opposition's demand for a neutral caretaker regime for election oversight.
Just before his arrest, Hossain described the polls as "stigmatised", saying it would not install any "legitimate government".
Political violence during strikes enforced by the opposition since November have left over 160 people dead.
Meanwhile, Hasina has asserted that her re-election in the much-disputed polls was legitimate and appealed to her arch-rival, Zia, to shun "terrorism" and sever ties with the fundamentalist Jamaat-e-Islami to strike a deal on the next elections.