North Korea says it arrested a US citizen for unspecified alleged crimes on 3 November.
Pae Jun Ho entered the country as a tourist, state media reported.
Some reports from South Korea have said the man is a Korean American who operates a travel company and went to the North guiding a group of tourists.
In recent years North Korea has arrested and released several US citizens, including journalists and Christians accused of proselytism.
State media said Pae Jun Ho was subject to criminal proceedings.
"In the process of investigation, evidence proving that he committed a crime against the DPRK was revealed," state news agency KCNA reported. "He admitted his crime."
It also said the man had met officials from the Swedish embassy. Sweden represents US interests in North Korea because Washington and Pyongyang do not have diplomatic relations.
The arrest comes amid tension between the US and North Korea over a recent North Korean rocket launch.