The United States leads that trend, with Western Europe and Japan only about two years behind. In the U.S., the number of people accessing the Internet through PCs will shrink from 240 million consumers in 2012 to 225 million in 2016. At the same time, the number of mobile users will increase from 174 million to 265 million.

In 2015, for the first time ever, there will be more U.S. consumers accessing the Internet through mobile devices than through PCs.

"In the consumer world, mobile Internet usage is already beginning to displace PC usage, and the United States is leading this trend," said Karsten Weide, program vice president, Media & Entertainment at IDC. "There has been much talk about how the future of the Internet will be mobile first and PC second. In the United States, that future is now."

Additional findings from the New Media Market Model include the following:

• Online PC activities will also be impacted as consumers take their usage mobile. IDC expects that the share of users accessing social networks such as Facebook on their PCs will decline from 66% in 2012 to 52% in 2016.
• Worldwide mobile advertising will almost quintuple from $6 billion in 2011 to $28.8 billion in 2016
• Worldwide business-to-consumer (B2C) m-commerce spending will grow six fold between 2011 and 2016, reaching $223 billion at the end of the forecast period

"The Great PC Exodus on the Internet is happening because the PC was never truly a consumer product," added Weide. "Many consumers use them because there was no better alternative. Now, with the huge and growing installed base of more user-friendly tablets and smartphones, there are."