The seizure and arrests have been made in a series of raids since Friday night in the southwestern city, Khulna-based RAB-6 chief Khondker Rafiqul Islam said at a media briefing on Saturday.
The RAB estimated the street value of 2.25kg cocaine at about Tk 225 million.
The six arrestees included cocaine-peddling ringleader Arifur Rahman alias Sagir.
"Sagir has been running operations from a rented house at city's Gagan Babu Road for quite some time now," said RAB-6 Commanding Officer Islam.
"Acting on a tip-off, the RAB arrested Rana on Friday night in possession of 230 grams of cocaine," Islam said.
Based on information given by him, Sagir was detained from his home in the city. Following Sagir's arrest, Bikash Biswas was detained from a village in Rupsha Upazila.
"The rest of the seized cocaine was found on Bikash. The others were arrested after interrogating him," said Islam.