Prostate? If it is only a drop or two, it is okay as long as you have no other related complaints. Remember, the sphincter shut at the base of the bladder i.e. At the base of penis. So, if the penis is engorged some, there will be a few drops still in it to pass especially as it shrinks back to normal. However, if this is more than a few drops, it may reflect a prostate disease, especially, if you're over50.
See below... This is known as "post-void dribbling", and is a common complaint. If it doesn't get better soon, I would suggest that you see an urologist for an examination.