Two missiles were fired on Saturday morning and one in the afternoon, the South Korean ministry said in a statement.
Officials at the ministry said they were “monitoring the situation and remain on alert”.
The launches come at a time of stalemate between the two neighbors following weeks of high tension earlier this year.
Saturday’s missiles were fired in a north-east direction, and did not pose the same threat as the intermediate-range missiles Pyongyang was believed to have deployed along its coastline last month.
It removed them from the launch site early in May, indicating a lowering of tension on the peninsula, a US official said.
Such launches are routinely carried out by North Korea.
Tensions were high last month amid threats from North Korea to attack Japanese, South Korean and US military targets in the region and restart a mothballed nuclear reactor that produced plutonium for its weapons programme.
Pyongyang also shut down an emergency military hotline with South Korea, and withdrew some 53,000 workers from the Kaesong factory zone on its border with South Korea.
The threats followed tough new UN sanctions imposed on North Korea in March after its third nuclear test, as well as annual US-South Korea military drills that saw nuclear-capable B2 and B52 bombers flown over the Korean peninsula.
Divided Korea’s fragile peace:
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