The job role of writing headlines varies between organisations, but, yes, there are plenty of organisations where it is written by someone other than main author of the article.
Wikipedia can't be relied on here, but it gives an [unreferenced] overview of the situation.
[a headline] is generally written by a copy editor, but may also be written by the writer, the page layout designer, or other editors.
While I don't attempt to give precise numbers, I think these examples are sufficient to show that it is "often".
This job description of Press Sub-editor gives a general idea:
[Press sub-editors, or subs] also lay out the story on the page, write headings and captions, and may be involved with overall page design.
New York Times explains:
Readers often assume that reporters write their own headlines. In fact, they rarely do. Most headlines at The Times, print headlines in particular, are written by editors experienced in the task.
The Guardian has an article What do subeditors do?, which explains some of the attributes of how they write good headlines.
The Hollywood Reporter is advertising for a Senior Copy Editor. Duties include:
Write headlines, deks, captions as needed to expedite copy flow
One journalist from The Sun was "aghast" at a headline that didn't match his story, showing they were written by different people.
He said he had described the claims against Liverpool fans as ‘allegations’ in his piece. Mr Arnold said it was then editor Kelvin MacKenzie who wrote the headline ‘The Truth’ above the story.
On the other hand, some organisations give more of a role to the journalist.
In 2009, at the Financial Times, the role was pushed from the subeditor to the author, which was a big enough story for the Guardian to report on it:
Financial Times reporters will have to subedit parts of their own stories, including writing draft headlines as the paper launches the next phase of its digital integration.