Yes, you can keep the same EIN:

You will not be required to obtain a new EIN if the following statements are true:

• A corporation files papers with the state to convert to an LLC and will elect via Form 8832 to be taxed as a corporation.
• The number of members in the LLC changes from more than one member to a single member.
• The number of members in the LLC changes from a single member to more than one member.
• A sole proprietor files papers to become a state recognized entity, organizes as an LLC, and will file Form 8832 or Form 2553 to elect to be treated as a disregarded entity or taxed as a corporation or small business corporation.