it is in the range of 1-3 %.more than that is considered high but can be achieved. higher ctr make your account subject ot termination by google program since it is automatic detection based. adsense experts claim you can make 100 dollar per day for ctr of 1% if you have 40,000 visitors per day and 0.25 dollar per click on average so 1% is not too bad. visitors is the most important. you must however improve the ctr after getting visitors by adjusting the appearance of ads such as color and text size.