A 3 year old not wanting to wear clothes is normal and it can sometimes just be a phase.
Although some kids have sensory issues and the clothes actually do really bother them and so they take the clothes off.
Some kids also just like to take their clothes off and diaper off because they like to get the reaction out of you.
If your 3 year old keeps removing his clothes then you need to put their clothes back on without laughing or giving them a reaction.
However if they are at home and have at least a diaper on or underwear on then it can be okay for the 3 year old to run around the house wearing just a diaper or underwear.
When I was 3 I used to remove my clothes and run around the house and yard when warm in just my diaper.
I would keep my diaper on but not my other clothes.
I also remember running out the door in cold weather wearing just a diaper and my dad had to chase me down and carry me back into the house.