Wow a few people actually knew what they were talking about!
Yes it's a dead spot in your pedal stroke, nothing to worry about, depending on how much slack is in the chain you feel your chain "give" some more.
I like to have a very little amount of slack in my chain. enough to where I notice my dead spots but not enough to be distracting.
Just work on pedaling in every direction, not just up and down, but forward and back aswell. make that full circle with your legs. :-)