It will not override what is in the Sim's action queue, so it can be canceled before the Sim is spooked.

This 'Be Spooked' interaction can be canceled. This causes the Sim to scream frantically and then run away, while some of his or her needs will be depleted. When this happens, the ghost will sneak up on the Sim and vanish and then jump up behind the Sim while moaning and laugh. Although playable Sims cannot interact with them, ghosts can 'Spook' living Sims. They take on the same appearance that they had when they died, except that they appear to be pale green-blue and transparent. They will usually hang around for a few hours doing nothing but just walking around while making windy noises. When they appear, eerie music will play indicating their presence. They can appear at any time between 12:00 am and daybreak but they don't always appear. Ghosts appear on residential lots that have the remains of a deceased Sim in a form of either an urn or tombstone.

3 The Sims: Bustin' Out (PS2/GameCube/XBOX).

Sims 3 sim is invisible