The U.S. is probably already in recession thanks to the fear-induced slowdown from the coronavirus, economist Alan Blinder said Wednesday.

"I wouldn't be one bit surprised if when we look back at the data, it is decided ... that the recession started in March," Blinder, a former Federal Reserve vice chairman and now a professor at Princeton, told CNBC's "Squawk Alley." "We won't know that. It takes months to get the data that would be relevant to a call like that. But it wouldn't be a bit surprising to me."

While a recession is often defined as two consecutive quarters of negative economic growth, there are other measures, such as dramatic changes in the unemployment rate, that also are considered. Ultimately, the National Bureau of Economic Research is the arbiter. The Great Recession was deemed to have started in December 2007, but the NBER didn't declare it until a year later.

Blinder said the cause of the current downturn is "fear of shopping" and being in public places where the COVID-19 strain can be spread.

"You can understand why people don't want to go to restaurants, shopping malls, not to mention travel," he said. "Spending on all of those categories has probably plummeted and much faster than our system catches it."