If I live in an apartment and am not on the lease, is it legal if my roommate is trying to have me leave in 30 daysl?

Since you paid rent (I assume), you will be considered to be might be considered to be a "sub-tenant" (and the roommate on the lease is the "sub-landlord"). Since they have the right to legally occupy the premises, they can file an "unlawful detainer" action (i.e. eviction proceeding). This means however that they need to comply with all legal requirements in order to get you removed. This starts with giving you written notice (typically 30 days) to vacate. If you remain after that time, they will then file suit in court. Once granted, you will either have to leave the premises by the specified date or the sheriff will remove you. 

In the meantime if your roommate undertakes any "self-help" remedies such as changing the locks, removing your belongings, etc, you could sue them for illegal eviction. What you can do now is to contact a tenant's right group or attorney who specializes landlord-tenant cases; they can best advise you of your rights under specific state law.

Note:  If you are an "official" tenant, the only way to have you legally removed from the premises is to have the landlord file for the unlawful detainer action. Having your name on a lease is not the only way that you may be considered to be a formal tenant of the landlord. In addition to being on the lease, you may have achieved the status of a tenant if the landlord accepted rent from you directly; if the landlord put (or allowed you to put) your name on the mailbox/doorbell, and/or if you rented the place together with your roommate and it was clear that you were both on equal footing.