is it just for attention seeking? do you react when she does start taking her clothes off?

I would probably try ignoring the behaviour, just keep her on the chair for whatever she did wrong first. Don't acknowledge that she is taking her clothes off, and she should realise that she isn't going to get a reaction from you and just sit there until her time is up. If she gets off the chair then don't look at her or talk to her, just pop her back on.

having said that I haven't had anything to do with the Naughty Chair yet so I could be completely wrong..lol
Thanks for that hun. I usually just ignore the behaviour when shes on there. She doesn't get off the chair (just undresses herself/moves the chair along the floor - has resulted in scratches on the floor)
We have gone from spitting on the floor when she gets put on there to undressing herself ah the joys of toddlers.