Computer obsessive’s good to go — that’s scary! (3)
I believe the answer is:
eek
'that's scary' is the definition.
(exclamation of fear)
'computer obsessive's good to go' is the wordplay.
'computer obsessive' becomes 'geek' (I've seen this before).
'good' becomes 'g' (abbreviation).
'to go' suggests deleting specific letters.
'geek' with 'g' taken out is 'EEK'.
(Other definitions for eek that I've seen before include "Alarmed expression" , "Cry of alarm" , "Expression of mild fright" , "Expression of surprise" , "I'm frightened!" .)