There is a similar question : "Netbeans - Turn off - wavy red underlines - How?" But It's for earlier version, doesn't apply any more.
I still want error to be underlined, just not in the comments, it's now underlined something like : "buffersize"
In NetBeans IDE 7.4 RC1 (Build 201309162201), you can disable spellchecking under
Tools → Options → Editor → Spellchecker tab
The settings refer to:
Screenshot:
Here is an example BEFORE and AFTER disabling HTML spellchecking.
before:
after: