Larry Summers, former Obama economic adviser and Clinton Treasury Secretary, told CNBC on Thursday he's been taken aback by the perceived connection between oil price weakness and stock declines.

"I've been a little bit surprised by the pattern in which oil prices have seemed to have been associated with declines in the stock market, even declines in the stock market outside of the energy sector," he said in a "Squawk Box" interview—adding that "on balance" cheaper oil is likely to be beneficial to the U.S. economy.