I'm wondering if OSHA posters are supposed to be posted at a restraunt (in the back office area, or some area like that).

My work does not have any such thing posted, in regards to laws and such. Is this legal? If not, what can I do?

For a list of posters required by California, you may look at the following link: http://www.dir.ca.gov/wp.asp

Also, for employers who may be interested in posters, they may wish to check out the link for the labor law posters at the top of this website.