The regulator's governor Fazle Kabir revealed the report on client harassment prepared for the 2015-16 fiscal year on Tuesday.
According to the report, a total of 4,530 clients of the country's 48 banks filed formal complaints about financial irregularities and client harassment over the year.
As many as 563 clients have accused Sonali Bank while 373 clients expressed their dissatisfaction with Brac Bank.
Around 56.7% of the complaints were made by clients of private banks, whereas the rest were against state-owned banks.
Another state-owned bank, Agrani Bank, ranked third with 291 complaints while Islami Bank Bangladesh Limited, Janata Bank and Dutch-Bangla Bank Limited bagged 268, 231 and 204 complaints respectively.