The Leading Economic Index rose 0.1 percent from April after gaining 0.8 percent in the previous month.
While the gain was marginal, the increase indicated a persistent economic recovery, Conference Board Economist Ataman Ozyildirim said.
"Despite month-to-month volatility, the LEI's six-month growth rate remains steady, suggesting that conditions in the economy remain resilient," he said.
"Widespread gains in the leading indicators over the last six months suggest there is some upside potential for economic activity in the second half of the year," he added.
The leading index compares current business activity with 2004, the year the Conference Board assigned a level of 100. In May, the Leading Economic Index rose to 95.2.