IBM said its cloud-based digital analytics platform, tracking shopping in real time, showed sales up 27 percent from last year as of 2300 GMT.
"All signs point to Cyber Monday being a banner year," IBM said on its Digital Analytics Benchmark blog.
"The multiscreen shopper is out in full force this year."
The number of consumers using a mobile device to visit a retailer's site was 20 percent, and 10 percent of consumers were using their mobile device to make a purchase, according to IBM.
"Apple continues to be a big winner with the iPhone driving more retail shopping than any other device with traffic reaching eight percent versus 6.5 percent and 5.6 percent for iPad and Android respectively," the blog post said.
The company based its data on "the industry's only cloud-based Web analytics platform that tracks more than a million e-commerce transactions a day."
IBM offered no specific forecast for Monday sales but on Sunday, the research firm comScore predicted retailers would take in $1.5 billion for the day, a jump of 20 percent.
Cyber Monday became a tradition several years ago, when consumers would wait until the Monday after the holiday weekend to shop using high-speed connections in their offices. Retailers typically offer big discounts on items ranging from electronics to apparel, but many have now extended these to cover the full weekend.
IBM's Craig Hayman said that although many consumers now have high-speed Internet at home, "Cyber Monday is more important than ever."
"Cyber Monday represents the new commerce reality the shopping experience as it is lived by people everywhere," he said in a blog post.
The hot Monday sales came after surveys showed heavy online spending for "Black Friday," the day after the US Thanksgiving holiday.
Online shoppers spent a record of $1.042 billion on Friday, surpassing last year's Black Friday haul by 26 percent, according to comScore.
A total of 57.3 million Americans visited online retail sites on Black Friday, representing an increase of 18 percent versus a year ago, the firm said.