Maybe the economy isn't improving as fast as many pundits seem to think.

Gallup's Economic Confidence Index dipped to an average of negative 2 for the week ended Feb. 22, down from positive 3 the prior week. A 27 percent total of Americans said the economy was "excellent" or "good," while 29 percent said it was "poor." That produced the negative 2 total.

This is the first sub-zero reading for the index since late December. Prior to that, the index was consistently in negative territory since Gallup began tracking it daily in 2008.

"It is not clear what is behind last week's decline in confidence, although quickly rising gas prices last week may have played a role, given that the drop in gas prices coincided with the rise in confidence in late 2014," writes Gallup's Rebecca Riffkin.

Gasoline prices have climbed a hefty 3 percent in the last week to a national average of $2.34 a gallon for regular. To be sure, that still represent a whopping 32 percent drop from $3.43 a year ago.

Meanwhile, the Conference Board's consumer confidence index slid to 7 percent this month to 96.4 from 103.8 in January.

Consumers represent the lifeblood of the U.S. economy, and that presents a problem, says Jim O'Neill, former chairman of Goldman Sachs Asset Management.

"When the U.S. consumer is starting to be more than 70 percent of GDP, as it's threatening to do again, the U.S. structural story is not as powerful as so many people seem to now believe it is," he told CNBC. "It was, but it's weakening."

The economy grew 2.4 percent last year, its strongest performance since 2010, and analysts expect an expansion of about 3 percent this year.

After the financial crisis, the country began to increase its savings rate and investment, with the importance of the consumer sector shrinking, O'Neill said.

But in the last year, it appears "the consumer is back to being king," he said. "In some ways, the reason we had the whole mess [financial crisis] in the first place is because the U.S. consumer was too much of the king."

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