Meta Keywords were at one stage a key part of the important meta tags to have on your website along with a title and description.
As time went by however they began to be abused by the early search engine optimization people and the search engines stopped using them
Now Matt Cutts of Google has gone on record to say these are no longer included in anyway as part of Google’s ranking signals.
Indeed some people believe that having meta keywords on your site at all can be a bad thing as they make it easier for your competitors to see the kind of terms that you are trying to rank for.
There is therefore no need to still use meta keywords. However if for some reason you do decide to use them, you want to make sure that you don’t use too many and that they are relevant purely to the content on the page where you have them.
Be warned though that if they are misused they could even harm your site, at least in Bing’s eyes where they have stated that they do still use keywords, but normally to establish whether a site is likely to be using spammy techniques.