Magdalena Prus, spokeswoman for the prosecutor's office in the western city of Poznan, told AFP the individuals were suspected of the "manufacture, processing, use of and trading in explosives".
Police raided 85 homes of customers of the Poznan-based online firm which is run by a 26-year-old chemistry student.
Behring Breivik is thought to have used the fuses he purchased to carry out tests or even for his July 22nd bombing near a government building which killed eight people in central Oslo.
After the bombing, the right-wing extremist systematically shot dead 69 people at a summer camp of the ruling Labour Party's youth wing on the island of Utøya.
According to the Polish daily Gazeta Wyborcza, Behring Breivik first contacted the firm in November 2010 to ask the price of a viscose fuse with a combustion rate of one centimetre per second.
The firm responded that one metre of fuse cost one zloty ($0.32), and arranged an order for 15 metres, for a total of 45 zloty including postage to Norway.
Polish police were tipped off about the company's role by their Norwegian counterparts.
Behring Breivik, 32, has confessed to his attacks.
In a 1,518-page manifesto he published on the internet just before the assault, he professed his hatred for Western democracy, saying it had spawned the multicultural society he loathed.