The index climbed after gaining 0.1 percent in April and falling 0.3 percent in March, the research firm said.
The index is a comparison to the average monthly index in 2004, which was assigned an index value of 100. For the eurozone, the index now stands at 107.3.
For the region, the index has made gains in four of the past five months, "providing reason for cautious optimism about the economic outlook for the second half of 2013," said Conference Board economist Bert Colijn.
"We could see a slow recovery before the end of the year, but confidence in the (eurozone) economy is still fragile and could be easily reversed if another episode of financial uncertainty occurs.", Colijn said.