There is one 국청 listed in the Naver dictionary.
국청: <역사> 조선 시대에, 역적 등의 중죄인을 신문하기 위하여 설치하던 임시 관아.
(A temporary court of law in the Chosun Dynasty that is set up to interrogate serious criminals like traitors)
Related to it, there is 국문하다 (interrogate) and 친국하다 (a king or a high official conducts an interrogation himself).
These are all dead words which might only appear in period novels and dramas. 국청 is even more obscure than the others.