The Consumer Prices Index (CPI) rose by 0.3% in the year to April 2016, down from 0.5% in the year to March.
From late 2015, the rate began to increase gradually from close to zero. The drop in April 2016 is the first fall since September 2015.
Falls in air fares and prices for clothing, vehicles and social housing rent were the main contributors to the decrease in the rate.
These downward pressures were partially offset by rising prices for motor fuels and for certain recreational goods and cultural services, and by food prices, which were unchanged between March and April 2016, having fallen between the same two months a year ago.