No, it will not be an offence under Section 138 of the Negotiable Instruments (NI) Act if the cheque was given only as security and not for repayment of a loan or liabilit.
Section 138 applies only when a cheque is given to repay a legally enforceable debt or liability.
If the cheque was given just as a security, and no payment was actually due at the time the cheque was presented, then Section 138 does not apply.