Oh, without hesitating it's a definite yes.
The scariest movie I ever saw was Poltergeist (yup, go ahead and laugh) and at the time it was PG.
And of course there's The Ring which was PG-13.
In fact, most R rated films are simply for gore, language and adult/sexual themes. In fact, if it weren't for all the F-bombs, Blair Witch Project, another very scary film, could have easily earned a PG-13 rating.