I found a mom cat and her 4 kittens. They look about 6 weeks old. I put them in my garage with food, water, litterbox and a blanket. The mom cat is laying under a dresser in the back. It seems like she might be hiding from her kittens. Why would she do that? She was'nt scared when I took her home in my car. Could the kittens be sick?

She is finding them what she thinks is a safe place. This is what mom cats do.

Where did you find them ?

Does she spend time with them grooming and nursing them?

I t may be simply that she is a new place and is picking out her comfort zone.
Depending on the age of the kittens, if they have nice little pointy teeth she may taking a break from being bitten while nursing.
Take one kitten to the vet and just have them determine age.
They likely will not charge you to just run one in and have a technician take a quick look.
It may very well be that they are old enough to start feeding kitten food.
How are the kittens? Plump? Active? Thin? Crying all the time?