The group acknowledged the attack "is affecting the operation of some of its services and processes" but insisted that "no impact on providing an ongoing energy supply has been recorded".
"Steps were quickly taken to protect business operation systems", an EDPR spokesman told Windpower Monthly.
As yet, the company has not disclosed any changes to operations on its renewables generation business to protect against future attacks.
"The cause and nature of the incident is under investigation in order to restore the affected services and operations as quickly as possible," he said.
EDP's actions to resolve the situation are being communicated to the relevant authorities, he added.
Group president António Mexia told the Portuguese press that no blackmail demand had been received.
EDPR's financial results for the first quarter of 2020 are due out on 7 May.