This paper proposes an efficient and secure identity based online and off-line aggregate signature scheme with random oracles. An aggregate signature privides a technique for combining n differents signatures of n different messages into one signature of constant length. The proposed scheme can be implimentated on Wireless Sensor Networks application. Security of the proposed scheme is based on difficulty of breaking Bilinear Diffie-Hellman problem (BDHP). The scheme is secure in random oracle models under the assumption of computational infeasibility of solving BDHP. It is existential unforgerable under adaptive-chosen-identity and adaptive-chosen-message attack In On-line/Off-line signature scheme, the signing process can be broken into two phases. The first phase, performed off-line, is independent of the particular message to be signed, while the second phase is performed on-line, once the message is presented.