It can be both. Please note that ~고 있다 in Korean isn't exactly English gerund or vice versa. e.g. 알다 = to know 알고있다 = to be aware of Pay more attention to the context instead. English gerund is something very special, and it isn't available even in other European languages known to me (German, French) If you read something in a foreign language, try not to translate it to English in your head. Try to accept and understand it in that particular language first instead, THEN write it down in the most naturally sounding English of yours. That will make the best translation by far, if you still need one. Trying to always have the "most accurate translation possible" will cripple your learning process significantly, especially if you are learning a REAL foreign language such as Korean, because there is virtually none.

듣고 있다 = (I'm) listening 노래를 듣는다 = listen to music 노래를 듣고 있다 = listening to music