The Global Investor Confidence Index (ICI) dropped 8.8 points to 115.1 in October, down from September's revised readings of 123.9.
State Street's ICI showed investors in Europe have become slightly more risk-averse, with the European ICI dropping 24.3 points to 115.5.
However North America's ICI increased by 5.9 points to 108.5, while the Asian ICI rose by 2.1 points to 99.5.
"European investor confidence had crested in September at an all-time high, so it is perhaps not surprising to see it come down somewhat this month," State Street Associates' Kenneth Froot, who developed the index with Paul O'Connell, said.
He added the dip may be due to concerns over deflation in the region.
"Although the European Central Bank has engaged in covered-bond purchases, German opposition to full-blown Quantitative Easing may have left investors wondering whether or not the ECB can do enough to combat headwinds to growth."
State Street Global Markets senior vice president Michael Metcalfe said the index showed the significance of weakness outside the US, which had an impact on the index despite a rise in the US.
