According to The Conference Board, a private research group, Americans' confidence in the economy made its biggest drop this month since October 2011.

May's Consumer Confidence Index was reported at 64.9, down from 68.7 in April. In October, the measure fell about six points.

A reading of 90 indicates a healthy economy. That level has not been reached since the end of 2007.

The May dip showed consumers still need more encouraging news before they can say the economy is truly making a comeback. The Conference Board's Ken Goldstein said the key indicator being looked at by consumers is jobs.

After picking up earlier this year, hiring slowed down in March and April. May employment figures are due out Friday, with an expected increase of more than 150,000 jobs.

"I think that's going to reinforce consumer sentiment that March and April were the aberration, not the trend," Goldstein said.

Goldstein said the May confidence figure could have been a lot worse.

He added, "Despite two back-to-back lousy jobs reports, consumer confidence is pretty much holding up."