All CTRs are safe as long as you don't break Google adsense rules. You could even theoretically have a CTR of a 100%, without getting in trouble as long as all your clicks come from genuine visitors that have an interest in the ads you're displaying in your website. Of course with a CTR of 20% Google are likely to be looking a little more closely at your site, but as long as everything is above board you should be OK. Good luck.
Normal Traffic : 10/20% CTR is just fine High Traffic < above 80k imp per day > : 4% , if your CTR is highr than 6% then ur likely to be suspended by google. you can use openx to rotate/filter ads
It depends on your traffic mainly. Organic traffic has much higher CTR when directed towards a highly targeted niche. Usually it's 7%. But as long as you're following the TOS, you should be safe.
Don't worry about people saying that High CTR is harmful. As long as the clicks ar legit, there is no problem. I've created my own Blogger Adsense Template which I've been using for more than a year now. Average CTR = 13%. It is great to get the maximum out of Adsense and I never had trouble!
Personally I never get CTR more than 10% of the overall report. My is 3%-5%. I need to do more to improve it
ctr (Click Through Rate) is obtained by dividing the "number of users who clicked on an ad" on a web page by the "number of times the ad was delivered" (impressions) so removing ads will not help decreasing or increasing the CTR