CTRs depend on so many factors... including the following and so many more: the vertical, your average position, the strength of competition, how well your ad is written, how close your ad matches the query, the match type of the keyword, seasonality, the day of week/time of day, the particular syndication partners that drive traffic to this keyword, what country you're in, who you're targeting, and more.
I'm recommend developing your own benchmarks per keyword (Impression to Conversion... combining CTR and conversion %) - then working to improve it.
within google analytics, there's a somewhat new benchmarking system, learn more here:
[google.com...]