Keyboard odd behaviour - blue focus box

Lately my mac highlight a specific area of the screen or input field, it is marked with a blue marking around it. It happens in Safari and mail and other places too.

When it happens I cannot use "Space" on the keyboard, if I need to type a "space" I can do that by pressing "OPTION+Space".

Does anyone know how I can turn this feature off, or tell me why it acts this way now?