At the closing bell, the Dow Jones Industrial Average was 8.18 points (0.05 percent) lower at 16,561.80.
The broad-based S&P 500 dropped 3.12 (0.16 percent) to 1,933.80, while the tech-rich Nasdaq Composite Index declined 12.08 (0.27 percent) to 4,389.25.
Market sentiment was dulled by a sharp 18.5 point fall in the ZEW German investor confidence index to 8.6 points in August, its lowest level since December 2012.