Fetching details from the dictionary...

frightening; scary
あの先生はおっかないので近づきたくない。
That teacher is scary so I don't want to get close.
子供の頃は暗い廊下がおっかなかった。
When I was a child, dark hallways were scary.
この程度のお化け屋敷はおっかなくない。
A haunted house of this level is not scary.