The Economic Sentiment Indicator fell by 2.7 points in the EU and by 2.3 points in the eurozone to 90.5 and 90.6, respectively, the commission said.
The decline was broad based. "In both zones the decline was driven by falling confidence in all business sectors, especially in industry and retail trade," the monthly report said.
The index assigns the 1990-2009 average a numerical value of 100. Numbers below 100 indicates confidence has fallen below that 20-year average.
The confidence index fell sharpest in Britain (down 4.7 points), Italy (down 4.3 points) and the Netherlands (down 3.9 points).
The index dropped 1.5 points in France, 1.4 in Germany, 1 point in Spain and 0.8 points in Poland.
Confidence dropped in all of the region's largest economies in the month, the report said.