The index had been trending lower, but May's gain is third increase in the past seven months.
The index is a comparison from 1985, which was assigned the value of 100.
In May, the index rose to 76.2, up from 69 in April.
In the most recent confidence survey, 18.8 percent of respondents to a survey that involves more than 5,000 households indicated they believed business conditions were "good," up from 17.5 percent in April.
Responses indicating a belief that business conditions were "bad" fell from 27.6 to 26 in the month.
The percentage of respondents indicating jobs were "plentiful," rose from 9.7 percent to 10.8 percent, while those indicating jobs were difficult to get fell from 36.9 percent to 36.1.
"Consumer confidence posted another gain this month and is now at a five-year high. Consumers' assessment of current business and labor-market conditions was more positive and they were considerably more upbeat about future economic and job prospects," said Conference Board Director of Economic Indicators Lynn Franco in a statement.