When your Systolic blood pressure is between 120 to 139 and your diastolic blood pressure reading is between 80 to 89 then you're blood pressure is high enough to be in prehypertension.
It's not dangerous but if your blood pressure gets that high you need to do things to get the blood pressure lowered such as taking a walk and even drink apple cider vinegar along with some honey lemon juice and warm water is a good natural tonic that can help you lower your high blood pressure.