Missing mortar between bricks

thats nothing, totally acceptable. u dont need to worry.

If you have a good look OP you will see the masons left mortar out btw some bricks....that is to allow water to weep out. So a few extra 'exits' from lightly mortared joints won't hurt anything.

Assuming thats not a brick near the ground (as Zamboni said) its no big deal. Its unlikely its a drain gap because it appears accidental not intentional and is not the lowest brick. It appears the mortar separated from the brick slightly when it was drying, you can inject some caulking if you like but it won't do any harm either way, the gap is far too small to become a problem. Keep in mind brick is a water reservoir cladding, it absorbs water, so such a small gap will not let in much more water then the brick would absorb from the rain, and its likely it only separated near the outside (and if it runs all the way though its still not enough to be a problem.
I personally would leave it alone, the caulking will start to separate years from now, you won't be able to easily remove old caulking to inject new caulking and the gap is more an aesthetic issue then a durability/weather one.

Z0RrO wrote: ↑I noticed the mortar joint is missing here and there on my brick wall. I am concerned about weather damage. Should I fixed it ?[IMG]http://i304.photobucket.com/albums/nn18 ... zmt2qb.jpg[/IMG]

Consider you got an extra weep hole buddy

http://en.wikipedia.org/wiki/Weep

Mayoo wrote: ↑Consider you got an extra weep hole buddy

http://en.wikipedia.org/wiki/Weep

I was just going to post this before I read your post! lol

LOL, that's nothing and it probably isn't even a "real" brick wall to begin with. You should see how some of my ~85 year old mortar looks but it's still fine.