Major Nur Ali, a police officer, said Sagal Salad worked for Radio Mogadishu.
"Three men armed with pistols killed (her)... We heard gunfire and we rushed to the scene, the gunmen had already escaped," Ali told Reuters.
"She was rushed to hospital but she died on the way. They killed her near a college campus where she studied. We believe al Shabaab is behind her killing."
Al Shabaab was not immediately reachable for comment.
Late last year, a female reporter who also worked for Radio Mogadishu was killed in a car blast. Two men convicted of the killing were executed in April.
Also in April, a government firing squad executed a former media officer working for al Shabaab for ordering the death of six journalists.
The al Qaeda-linked al Shabaab was forced out of Mogadishu by African Union peacekeeping troops in 2011 but has remained potent, launching frequent attacks in its bid to overthrow Somalia's government.
Somalia was plunged into anarchy in the early 1990s following the toppling of military dictator Mohamed Siad Barre, and has been struggling to reconstruct.
Somalia ranked 172nd out of 180 countries in the 2015 Reporters Without Borders press freedom index.