If it is one of those on this list of common lockcodes from Lifehacker then you should probably change it ASAP. This illustrates the difficulty that many people seem to have in memorising even simple passwords and codes.
What is mine? Actually I have two and neither is in that list. One is from a sequence that has meaning to my family so we use it for the iPad and other things like hotel room safes. The other I use for my iPhone, I learnt it as the door code for an office I worked in some years ago and it stuck somehow.