Research firms International Data Corp. and Gartner don't agree on actual sales figures, but they do say Mac sales slowed to their lowest rate since the third quarter of 2013, the paper said.
Gartner estimates Apple's Mac sales contracted by 1.5 percent, while IDC says the slow-down was more drastic at 3.4 percent.
The slowdown came as the overall PC market shrank by 11 percent in the third quarter, according to IDC. Apple's share in the PC market grew, however, because other companies fared worse during the quarter.
The Journal said both firms attribute the decline to shipments outside of the United States, which were hurt by a stronger dollar.
Apple did not immediately respond to a CNBC request for comment. It is set to report earnings on Oct. 27.
Read the full Wall Street Journal story here.