The building society commissioned a survey of more than 1,500 Britons, which was conducted by research firm Opinion Matters.
Researchers found that 77% of respondents said one of their main reasons for going online was to service their bank accounts, while just 58% cited social media as one of their top incentives for logging on.
Other common reasons for going online included shopping (77%), looking for holidays (65%) and job searching (37%).
Richard Searle, Nationwide's head of channel integration, said that online banking had "really taken off" over the past few years.
However, he admitted: "Even we were surprised to see it beat social media (e.g. Facebook) as one of the top reasons the nation goes online."
Mr Searle also noted that women and men appear to have very similar online habits, with 79% of male respondents and 76% of females using online banking services.
He added that the research "has also shown the amount we now all use online banking as part of our day-to-day lives, with a quarter (25%) of us going online two to four times a week and 12% going online once a day".
Britons' faith in online banking may well increase in the near future, after recent figures from Financial Fraud Action UK revealed that online banking fraud losses for January to June 2011 were 32% lower than the losses recorded in the first half of 2010.
Banks' increasing use of fraud detection software and greater consumer awareness of the need for security measures are thought to have contributed to the fall.
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