That's according to the latest figures from industry measurement body Barb, which carried out a study of 11,500 viewers over a week in November 2011.
Almost 15% of respondents to the Barb study said they watched TV online – a rise of only 0.5% compared to November 2010.
But viewing on smartphones continued to rise, with around 3% of those questioned saying they had watched TV on their mobile phone, up from 1.9% in November 2010 and 1.1% in November 2009.
Barb says the "plateau" in online viewing via PCs could be attributed to the rise in digital set-top boxes and the boom in popularity of catch-up services on internet connected TVs, such as Sky+ and Virgin TV On Demand.