Short answer, no.

Longer answer, kind of.

North Korea, the state, until 1996, did not ever claim responsibility for a terrorist attack that they perpetrated.

They have claimed responsibility for a few things, though.

They claimed responsibility for the 1969 EC-121 shootdown. This was a military action against a military target and the North Koreans claimed that the US plane was deep inside of their airspace and that it was an act of war that they retaliated against. The earlier Pueblo Incident was pretty much the same thing - the North acted in self defense against imperialist aggression, yada yada yada...

If you look at other military incidents, they follow the same pattern. North Korea simply claimed that they were stopping the enemy or reacting to a provocation. IMHO, we can't really say that they "claimed responsibility" for these actions. "Claimed responsibility" implies that we don't know who did it.

In that case, again, North Korea has not claimed responsibility for a terrorist action or an overt aggressive act of war. However, Kim Il-sung did apologize for the Blue House raid of 1968. In 1972, the head of the South Korean CIA, Lee Hu-rak, went to Pyongyang on a secret meeting where he met Kim Il-sung. Kim apologized for the Blue House raid, claiming that it was "extreme-leftists" in the government that organized it and it was not his wish. For a great analysis on why Kim was probably full of shit when he said that, check out North Korea's Military-Diplomatic Campaigns, 1966-2008 by Narushige Michishita, as well as Scenes from an Unfinished War: Low-Intensity Conflict in Korea, 1966-1969 by Major Daniel P. Bolger.

TLDR - North Korea has not apologized for any of their terrorist activities. Kim Il-sung did apologize, but he also claimed it wasn't his fault which is most likely not true. North Korea has admitted to their military actions when it's obvious, but they always claim justification.