The Fed will view the first decline in the CPI since March as "further proof that price pressures are building more slowly than some have feared."
"The inflation picture is still fairly tame, certainly not heating up enough to push the Fed to a more aggressive stance."
Inflation continued its "slow but steady" climb in May as Fed policymakers gear up for another hike in interest rates.
"We expect a continued rise in inflation to prompt Fed officials to raise rates four times in total this year,” one economist says.
Inflation appears to have "re-emerged after a long period of dormancy," fueling fears that the Fed will raise interest rates more aggressively this year.
Last month's CPI data "was very muted and not something which the Fed is going to be happy to look it," a market analyst says.
"It is getting harder for the Fed to continue claiming that this is a temporary drop-off," an economist says.
The April increase matched economists' expectations and suggests the March decline was "an aberration."
Fed Chair Janet Yellen says the firmer pace of inflation has "strengthened" the case for an interest rate hike next month.
It was the fourth straight monthly gain but food prices dropped 0.3% and inflation remains low by historical standards.
The Consumer Price Index falls 0.1% in August, highlighting the interest-rate dilemma facing the Federal Reserve.
Despite the tame inflation trend, signs of an improving economy may keep the Fed on course to hike interest rates this year.
