Two men shot dead Rahmo Abdukadir, who worked for the private Radio Abduwaq station, late on Sunday.
“One of our female staff members was shot and killed in Mogadishu,” said radio station director Abdikarin Ahmed.
“We don’t know why she was killed but we are in shock,” he added.
Witnesses said men approached the reporter before firing repeatedly and then running away.
“Two men armed with pistols shot the woman… they fired their guns five times before fleeing,” said witness Abdi Moalin Shire.
“There was another girl who accompanied the victim but the gunmen did not target her, she ran away screaming for help,” said Issa Mohamed, another witness.
At least 18 media workers were killed in 2012 – double the worst year on record and second only to war-torn Syria – but no one has been charged with the killings.
Abdukadir is the third journalist to be killed this year.
A journalist for Mogadishu’s Radio Shabelle was shot dead in January, while another journalist was killed when he was caught up in a suicide bombing in the capital earlier this month.
Somalia’s journalists have suffered a string of attacks, including assassinations or bomb blasts often blamed on Al-Qaeda-linked Shabaab insurgents.
Other murders are also believed to be linked to struggles within the multiple factions in power.
Last month Somalia’s government offered a $50,000 (37,000 euro) reward for information leading to the “successful conviction of a journalist killer”.
Somalia has been ravaged by conflict since 1991, but a new UN-backed government took power last year.
Many have said the new government offers the most serious hope for stability since the fall of dictator Mohamed Siad Barre more than two decades ago.