And 70 per cent actually use their devices while they watch the box.
Americans consumed an average of 2.4 hours worth of media a day via their mobile devices in Q2, outpacing TVs on 2.35 hours and PCs on 1.6 hours, according to mobile ad network InMobi.
Mobile may only be outshining TV viewing by a sliver, but it's likely stimulated by the 70 per cent of Americans using phones and tablets while watching TV.
Two-thirds say they prefer to use their mobiles because they're easy to use, while 56 per cent say the devices are always with them.
Mobiles are supporting 71 per cent to use mobile search, 64 per cent to browse the internet, while 77 per cent tent to use the gadgets in bed, and 65 per cent do so when waiting for something.
Results show that females actually use the devices more than males, with particular spikes experienced when in bed and shopping, with respective percentages of 84 per cent vs 70 per cent and 40 per cent v 26 per cent.
Anne Frisbie, VP and MD of North America for InMobi, said: "We expect the trend of ever increasing media consumption on mobile devices to continue, and even accelerate as advances in mobile rich media deepens user engagement by offering a better overall user experience.
"Marketers are taking notice and are increasingly investing in mobile to target consumers where they are spending most of their time consuming media."