In most cases, no.
You should first pay attention to the duration of the contract.
Agreements of indefinite duration may always be terminated by giving a “reasonable” notice period, even if not stipulated in the contract. On 28 June 2019, the Belgian Court of Cassation dismissed the appeal lodged by the applicant who argued that a contract for an indefinite period may only be terminated with a notice period if the agreement at stake contains such a provision or if the termination is wrongful. That being said, the parties may provide in the contract for the duration of this notice period. The latter, however, does not preclude the possibility that this specific duration might be challenged in court at a later stage.
Such termination is, in principle, irrevocable. However, in its decision of 8 February 2018, the Court ruled that, because of the principle of contractual freedom, both parties can decide to disregard it afterwards.
On the other hand, a contract for a definite period cannot, as a rule, be terminated unilaterally unless otherwise agreed between the parties or permitted by law (e.g. article 1794 of the Belgian Civil Code). In its decision of 7 June 2012, the Court found that the terminating party may withdraw a termination notice that has been disputed by the other party, provided that this withdrawal doesn’t occur in an “improper” way, i.e. “mits hij dit recht niet op abusieve wijze uitoefent/ à condition de ne pas exercer ce doit de manière abusive”.
These rulings (C.18.0410.N, C.17.0255.N and C.11.0449.N) can be found on http://www.juridat.be