A mineral material processing plant and a method for controlling thereof. The processing plant includes at least one motor, at least one actuator, a control and adjusting system, a switch for switching the processing plant to a standby mode and an arrangement for keeping selected actuators in operation with a reduced standby speed. In the method, a command is given to the processing plant to switch to the standby mode and in response to the command to switch to the standby mode, feeding of mineral material to the processing plant is limited and speed of the motor or motors of the processing plant is reduced from the processing speed (Rf) to a reduced standby speed (Rsb) and it is ensured that selected actuators of the processing plant remain operating with a reduced speed.