you should be able to just import the file (or drag it to the project panel), then just drag it to your comp.
you may also need to make sure that audio is enabled for preivews… ithink it’s in compostion>previews, make sure there is a check mark next to audio.
i would, however, recommend converting it to a .wav or aiff to use with in ae. mp3s and other compressed audio files can behave inconsitently with in ae.
Kevin Camp
Senior Designer
KCPQ, KMYQ & KRCW