Is it ok to listen to music during the Omer?

The widespread custom is to refrain from live, joyous instrumental music during Sefiras HaOmer as a sign of mourning for Rabbi Akiva's students. Communities differ on the details — some are lenient with recorded music, a cappella, or for exercise and simcha-related needs — so the honest answer is: follow your family's minhag and ask your own rav for the particulars. The spirit of it is to carry a little restraint, a little awareness that these are days of mourning, into your everyday listening.