How do i tell them to mind their own business?

I'm a new joiner at my workplace, and my male (and female) co-workers keep prying into my private life, asking me if I have a bf or not. I don't currently have a bf, but at the same time, I don't want to talk about my love life with people I work with as I don't think its anybody's business. I don't want to come across as rude or secretive, so how do I tell these people to mind their own business? I'm thinking I should just say I have a bf then hope they stop gossipping and leave me alone but I don't want to lie either...Help!