Bicycle Mechanics - uneven chain tension?

i have a single speed bicycle and is it normal for the chain tension to be uneven? when i turn the bike upside down and i spin the pedals slowly some parts of the chain are more "tighter" (less up down movement when pressed against) then other parts. is this normal or is there something wrong with my chain?

It's common. The issue is that it's very hard to get the front chainring exactly concentric with the crank.

One wat to possibly resolve this problem is to loosen the chainring bolts just enough so it can move a wee bit. I say possibly, because it depends upon overall tolerances. Anyway, rotate the chainring, noticing the tight spots. Gently tap the chain with a piece of wood or a rubber mallet. Keep doing this until the chain tension is as even as you can get it. Now, tighten up the chainring bolts good and tight. This is also a technique for tandem timing chains, only in that case you loosen both chain rings.

If Hammer's suggestion doesn't work then your chainring isn't perfectly round, happens with a lot of BMX chainrings when they've seen a lot of abuse/old age [I work with a BMX racer], same thing goes for single speeds especially if its an old steel ring - if your chainring is really old that could be it as well and will just have to get a new one - but Hammer's suggestion is usually the solution - good luck