In November, headline inflation hit 10.1percent as food and fuel prices went up.
But two fuel price slashes in recent months have helped to ease pressure on prices.
In its December inflation update released on Friday, NSO said headline inflation eased by 0.2 percentage points from 10.1percent to 9.9 percent.
The development means inflation averaged 9.2percent in 2018 as compared to 11.5percent in 2017.