We're frequently asked about Meta Keywords and whether they should be used to improve SEO.
The short answer is no, don't bother with Meta Keywords.
The Keywords meta tag used to be used in the early days of search engines. However, they quickly became useless to search engines as they were abused.
Major search engines such as Google dropped support for Meta Keywords back in 2009.
Here's the announcement from Google back in 2009 that they no longer used Meta Keywords in ranking.
It's possible that Yandex, the Russian search engine, may still use them as they do list it in their documentation here. If you're looking to get on Yandex for Russian searches then you can still use the Meta Keywords feature in All in One SEO.
However, if you're primarily concerned with ranking on Google and Bing then you don't need to worry about adding Meta Keywords to your site.