The invention relates to a method for allocating radio resources to a mobile terminal for data transmission in a mobile communication system as performed by a mobile terminal and a base station, respectively. Moreover, the invention relates to a mobile terminal and a base station to perform such method, as well as an implementation of the method in software. The invention further provides a mobile communication system in which radio resources are allocated to a mobile terminal for uplink transmission. In order to avoid false activation of a semi-persistent resource allocation the invention defines new conditions under which a mobile terminal activates a semi-persistent resource allocation. Unlike for example in prior-art systems, a mobile terminal only activates a semi-persistent resource allocation, if it can confirm the activation command received from the access network. Preferably, the activation command and its confirmation are resource assignments.