looks like mint rust.
i got this from another post:
* Posted by Daisyduckworth NSWAust (My Page) on
Fri, Jul 8, 05 at 18:11

Mint rust is a fungal disease. Take the mint out of the pot, wash the plant and the pot in warm soapy water (washing up detergent will do), and discard the soil wrapped in plastic and into your bin. Repot using fresh potting mix.

Another way to do it if the pot isn't plastic, is to cover the plant with straw and set the straw alight (taking all precautions, of course!). The fire will destroy the fungus, but will not kill the roots of the plant, which will come back soon enough.

Stick an old rusty nail into the new soil - mint likes iron.

also what i saw is that it rarely kills the plant, but it looks unsightly

I've never seen mint rust, but have you looked carefully at the undersides of the leaves for spider mites? They often attack plants that are dry and stressed. The discolouration looks like it could be spider mite stippling/sunscald. Tap the leaves over a white piece of paper, look closely and let us know. Spider mites can infest half the garden before you realise they are there.

If it is spider mites, spray with Garlic Spray.

Thanks re: mint rust but I don't think I want to set my plant on fire..

I looked at the underside, there appears to be little white things, some small webs... I guess these are spider mites? I think that's what the problem is. I'm almost certain. I looked up spider mites and it looks pretty similar to the underside of my plant. That would make sense if they attack dry and stressed plants as I haven't watered in a long time... But I will water properly from now on!

Can I make garlic spray myself? I have a juicer...

Thanks!

It helps to remove and trash the worst infected parts of the plant. Keep it in part shade and water the heck out of it. Horticultural oil smothers mites if it is easier to get than making garlic spray. Whenever you apply oil in any form keep the plant out of direct sunlight for a week. Good luck!