Local Telemundo affiliate KVEA Channel 52 announced the probe two days after it was first revealed that Villaraigosa, whose wife has filed for divorce, had been in an extramarital affair with Salinas for about a year.
"As we have stated, we are committed to journalistic excellence," Manuel Abud, KVEA general manager said in a statement to news media. "Given the seriousness of the allegations that have been made, we have decided to conduct an internal review of the decisions and events that led us to where we are today.
"We will conduct this investigation with the utmost respect to personal privacy and journalistic standards."
The mayor's office had no comment, Villaraigosa spokesman Sean Clegg said.
Salinas said in a statement that she would cooperate with the investigation.
"I welcome Telemundo's decision to conduct a comprehensive review of the matter and respect their desire that I allow the review to be completed before returning to work," Salinas said.
"I am confident that when all the facts are analyzed it will be clear that I conducted myself in an appropriate way."
Salinas once covered the mayor as a political reporter. Telemundo took her off the political beat about 11 months ago.
Still, as the station's news anchor, Salinas read an on-air report last month on the mayor's separation from his wife. At the time, Villaraigosa declined to say whether he was involved with another woman.
"It's a little late, but good for them," said Kelly McBride, ethics group leader at the Poynter Institute, a journalism foundation in St. Petersburg, Fla.
McBride said the station should bring in an outside expert to help conduct the investigation. She said the probe should have been conducted when station mangers first learned of her involvement with the mayor 11 months ago.
Any investigation must also ask what role her managers played, McBride said.
"The investigation should include not just what stories did she influence, but who knew and when did they know and what were their decisions," McBride said.
Since confirming his romantic relationship with Salinas at a news conference on Tuesday, Villaraigosa — the mayor known for being everywhere — has disappeared from sight.
The famously ubiquitous mayor had no public appearances on July Fourth — usually a day for politicians to make the rounds of parades and fireworks displays. Even though he is a national co-chair of New York Sen. Hillary Rodham Clinton's presidential campaign, he skipped the official opening of her Los Angeles headquarters.
He had no events Thursday, and is not expected to appear in public until next week.
The mayor "deserves a few days' vacation during a holiday week to attend to personal and family matters," Clegg said.