From MusicBrainz Wiki

Here are a list of some arbitrary popular artists that Last.FM doesn't have MusicBrainz IDs for. If anyone wishes to try and add these artists to MusicBrainz, this would be much appreciated! If any of these artists are already in MusicBrainz, please add a link to the MusicBrainz artist. If you create a new artist (because MusicBrainz didn't have the artist) again - please link to the new artist. If the artist shouldn't be in MusicBrainz at all (ie, collaboration, should be handled with artist credits), you can just delete the row.