The helicopters are upgraded versions of Mi-2s, as well as Mi-4 and Mi-8 troop carriers, and some are armed with machine guns and rockets, Chosun Ilbo reported.
Baeknyeong Island is South Korea's northernmost island, just south of the maritime border with North Korea in the West Sea.
Since Kim Jong Un assumed power in North Korea last year, Pyongyang has deployed rocket launchers, hydrofoils, Mi-2 helicopters and fighter jets along the western coast and conducted military drills, Chosun Ilbo said.
"There are no signs yet that North Korea is seeking to stage a provocation," a military official said. "But since the ouster of North Korean army chief Ri Yong Ho, there may be some instability in the North Korean army, so we have stepped up our preparedness."
Meanwhile, North Korea upped its campaign critical of the South's President Lee Myung-bak, with state-run television airing images of North Korean soldiers shooting at paper targets marked with Lee's name and campaign phrases, Yonhap reported.
North Korea's state-run media Korean Central Television Monday aired a program featuring security soldiers accusing the Lee administration of orchestrating an attack on the statues of North Korea founder Kim Il Sung and pledged revenge for what they claim is an "indiscriminate scheme."