Arguably, yes, because you haven't really broken your data down as much as you need to; but this is a fairly contentious issue - just see http://en.wikipedia.org/wiki/First_normal_form#Atomicity. If you are frequently needing to query inside data, you may well gain from moving that 'prefix' into a separate column, or more drastically rethinking your data model if that's appropriate.

In this example prefix is something the user typed in. So textcolumn LIKE '%blahblah%'.