Green’s Dictionary of Slang

(Ulster) nosy, inquisitive.

1932		Ulster Hiker June n.p.: I should advise the ‘nebby’ (forward) hiker to have a ‘crack’ with the first ‘knowin’ Ulster ‘gaudsman’ (plough-driver) he meets [BS].
1951		L. Brown Iron City 38: Why did they arrest you, if you don’t mind me being so nebby?
1979		J. Morrow Confessions of Proinsias O’Toole 88: ‘Houl’ hard, Duncher, houl’ hard,’ I pleaded. ‘I don’t want you to think I’m being nebby, but I have to get things straight.’.