I have a couple tomato plants that have small yellow spots on the leaves. These plants are about 6 weeks old. I'm planning on transplanting them to my garden this weekend. Any idea what caused this and is it something I should be worried about?
It looks like rust, which is a type of fungus.
There are many species of rust but this could be common rust - Phragmidium spp.
You should remove these leaves if you suspect it is rust to avoid further contamination.
Tomato plants don't like their leaves to get wet so you should water the soil not the leaves.
Looks like you are growing indoor under led lights, make sure there is enough ventilation.
More info here: https://www.planetnatural.com/pest-problem-solver/plant-disease/common-rust/ and do some more research on rust fungus which is quite common in gardening.