Yes, it is possible to overdose your cat or dog on Frontline if you accidentally double dosed or were administered an amount that is in excess of that prescribed for its weight.
Some dogs are quite sensitive to the product can become overly anxious and scratch or bite themselves when they have been given too much. Other dogs may not be sensitive to an overdose at all.
If you fear that you have given your head too much Frontline, I would recommend taking a wait-and-see approach before seeking help from the veterinarian is there is not much that can be done once it has been administered.
If has been less than 24 hours since you have put the Frontline on your dog, you can thoroughly clean and wash them in order to get as much of the product off of his body as possible, but the chemicals are wicked into the hair follicles fairly quickly.
In most cases it will not be necessary, but if your dog has a strong reaction to the overdosing and you will need to seek medical attention from your local veterinarian.