Motorcycle-riding gunmen attacked Rogelio Butalib, 44 in the southern city of Tagum on Mindanao island, said regional police spokesman Chief Inspector Jed Clamor.
"We are looking at the possibility that he was killed because of his profession," Clamor told reporters.
Butalib was a commentator for the local Radyo Natin station and may have made enemies because of his programme that tackled various local issues, including corruption, Clamor said.
However, the police official said the killing could have been politically motivated, because the victim was also elected to a hotly contested district post in October.
Butalib was the third journalist shot and killed in the southern Philippines in two weeks.
Michael Diaz Milo, a talk show host for DXFM radio, was killed in the city of Butuan Friday, while broadcaster Joas Dignos was murdered in the city of Valencia on November 29.
Unidentified gunmen shot and wounded a fourth radio journalist, Jonavin Villalbal, in the central city of Iloilo late Tuesday.
The suspects in all four attacks remain at large, police said.
"This is saddening and frustrating. Another one from our ranks is killed," Rowena Paraan, chairwoman of the National Union of Journalists of the Philippines, told AFP.
She urged authorities to solve the murders quickly and condemned the apparent impunity for those who carry out the attacks.
The New York-based Committee to Protect Journalists ranks the Philippines as the third-worst in its "impunity index" of countries that fail to combat violence against the press.
By its count, the committee has said at least 72 journalists had been killed in the Philippines since 1992, excluding the three latest deaths.
In November 2009 32 journalists were among 58 people kidnapped and massacred in the southern Philippines, allegedly by members of a powerful Muslim clan.
Of the 196 people charged in that case, 88 remain at large, and rights groups said families of the victims as well as witnesses remain under threat of retribution.
Four years after the killings, no one has yet been convicted. Despite recent moves to speed it up, the trial is expected to drag on for years in the country's overburdened court system.