I feel uneasy about signing a contract that states that I am an "at will" employee. I feel that there is no job security . can this be avoided?

Most employees are at will and yes, they enjoy less job security than those who have employment contracts with definite terms and/or restrictions on termination.  However, assuming that you do not have such an employment agreement now and are therefore employed at will, not signing the agreement will not change your status - you will still be at will - and your employer has the right to fire you (or not hire you in the first place, depending on your status) if you don't sign the agreement.