It is very common, I think it just means that you are getting ready to ovulate, or did ovulate. I usually have that somewhat myself each month for a day, and then it stops.
If it doesn't stop, and just continues until you work yourself into a real period, you could have a lack of progesterone in the second half of your cycle. I've had that too and had to take Provera each month for 10 days in the second half of the cycle.
I wouldn't really worry, though, if it's just a bit of spotting for a day or so; but you might check with your doctor if it's bugging you.