The problem you are describing can be related to a number of factors and variables- so the answer also depends-- on your muscle, on how deep the wrinkles are, on your skin type and the amount of spacing of the Botox used. The best thing to do is discuss your result with your plastic surgeon...
This is often called a Spock or a Jack Nicholson and happens with some frequency.
It occurs because the medial portion of the frontalis has been knocked out but the lateral portion is intact. When you lift your brow, the lateral portion lifts and the medial does not, creating the scary...
Excessively arched brows after Botox injection are typically very easy to resolve. The so called "Nicholson" brows (referring of course to Jack) are easy to relax - a few units of Botox (probably in the range of 2-4 units) are placed in the upper forehead on both sides and this relaxes...