An official said earlier that 11 Japanese companies in the auto industry violated the law but none had been publicly identified.
Regulators have disclosed few details about the basis for their investigation but one agency said Mercedes Benz was guilty of "vertical price-fixing." It said the company, a unit of Germany's Daimler AG, used its control over supplies of replacement parts to charge excessive prices.
That appeared to confirm suggestions Chinese regulators were motivated by complaints about the high price of imported luxury vehicles and replacement parts.
NSK supplies ball bearings and other components to auto factories in China.
Officials have said Volkswagen AG's Audi luxury unit and Fiat Chrysler Automobile NV's Chrysler also violated the law. Toyota Motor Co. has said its Lexus unit is under scrutiny.
Business groups welcomed the enactment of China's anti-monopoly law in 2008 as a step toward clarifying operating conditions. Since then, they have said it is enforced more actively against foreign companies than against local rivals.
Regulators also have announced investigations of Qualcomm Inc., a San Diego, California-based maker of chips used in mobile phones, and software giant Microsoft Corp.
Last year, Chinese regulators fined five foreign dairies and one from Hong Kong a total of $108 million on charges they violated the anti-monopoly law by setting minimum prices their distributors were required to charge.