In October, millionaire investor confidence surged to its highest level in nearly three years.

According to Spectrem Group’s Millionaire Investor Confidence Index, which was released Wednesday, rose six points in October to zero. The increase keeps the index in neutral territory and brings it to the highest level since December 2007, when it stood at eight.

Meanwhile, the Spectrem Affluent Investor Confidence Index, which measures the investment confidence and outlook of households with $500,000 or more in investable assets, rose three points in October to minus-13, a mildly bearish reading.

"While the stock market's October gains clearly contributed to this positive trend, underlying economic fundamentals remain a top concern for America's wealthiest investors," said George H. Walper, Jr., Spectrem’s president.

In response to an open-ended question about the factor most affecting their investment plans, affluent investors in October cited: Stock market conditions (21%); the economic environment (20%); retirement (10%); household cash flow (10%); the political climate (8%); and household income (2%). Those citing the economy declined from 22% in July, the last time this question was asked, while those citing stock market conditions remained unchanged.

Millionaires were slightly more focused on stock market conditions (22%) and on the economic environment (21%) than the affluent.