The Markit/Nikkei services Purchasing Managers' Index (PMI) for Japan decreased to 51.2 in February from 52.4 in January.
A reading above 50 indicates expansion in the sector, a reading below 50 indicates contraction of activity.
The index was mainly driven by declines in new business and employment.
"Latest survey data pointed to a general slowdown of growth in the Japanese service sector. Business activity and new order growth both slowed, leading to an easing in the rate of staff hiring," economist at Markit, Amy Brownbill, said.