Expectations had been high that Pyongyang would carry out a test to coincide with celebrations marking the birth of North Korea's late founding leader Kim Il-sung on April 15 but it did not materialise.
The North Korean military last week moved two launchers believed to be for Scud missiles to the northeast province of South Hamgyong, Yonhap news agency said, citing a senior Seoul official.
"We have discovered the North has moved two additional TELs (transporter erector launchers) to the east coast ... after April 16," the official was quoted as saying on Sunday, adding Seoul and Washington were closely monitoring the site.
A spokesman for Seoul's defence ministry was not immediately available to confirm the report.
Previously, the North was reported to have moved seven missile launchers to its coast facing the East Sea (Sea of Japan) in apparent preparations for a test that would further escalate tensions.
Angered by fresh UN sanctions triggered by its third nuclear test in February and joint South Korea-US military exercises, the North has for weeks been issuing threats of missile strikes and nuclear war.
But despite the passing of the Kim Il-sung anniversary, a Seoul defence ministry spokesman said Thursday that the possibility of a test involving shorter-range Scud, mid-range Musudan, or long-range Rodong missiles remained.
April 25 could be another possible date for a missile launch, the report said, quoting military officials in Seoul. That is the founding anniversary of the North's military.
The Musudan - seen as most likely to be tested - has an estimated range of 2500 to 4000 kilometres, enough to reach South Korea and Japan and potentially US military bases on the Pacific island of Guam.
US President Barack Obama has expressed doubt over the North's capabilities, saying last week he did not believe Pyongyang could yet arm a missile with a nuclear warhead.