It was previously revealed that Gibbs (Mark Harmon) and his team will be hunting the psychopathic Port-to-Port killer in the current run's final episodes.
De Pablo told Entertainment Weekly: "We know that [the finale] has something to do with the Port-to-Port killer. We know that something awful is gonna go down, like always. And we're all deathly terrified."
The actress admitted that the potentially grim events of the finale are taking their toll on the show's cast.
"Everyone is dealing with it differently," she suggested. "We may not be aware it's a stressful situation, but we're all going through it in our own way."
The eighth season of NCIS is currently expected to conclude in May. A ninth run has already been commissioned, after the show achieved a ratings high of 22.85m viewers last month.
The show continues on Tuesdays at 8/7c on CBS.
> NCIS star teases new team members