The price cut for the Xbox 360 model with the 20 gigabyte hard drive will come before the video game industry's biggest trade show, E3, taking place in Los Angeles on July 15-17, the report said.
A Microsoft spokeswoman declined to comment on the report.
Microsoft last cut the price of the Xbox Pro in August, from $399 to $349, prior to the release of Halo 3 the following month.
A cut to $299 would make the Xbox 360 Pro $100 less than one of the console's major rivals, Sony's PlayStation 3 with a 40GB hard drive.
Microsoft is locked in a three-way competition with Nintendo's Wii and the PlayStation 3, which comes with a high-definition Blu-ray video player.