"On the basis of information received from foreign authorities about the attack in Berlin on December 19th,... (Switzerland's) Office of the Attorney General (OAG) has opened criminal proceedings against persons unknown," it said in a statement.
The OAG said it was probing suspected violations of laws prohibiting organizations such as the Islamic State group and Al-Qaeda, and banning the support of or participation in criminal organizations.
It said it was working closely on the case with Swiss federal police (Fedpol) as well as with "foreign authorities", but provided no further details.
The Islamic State group has claimed the Berlin rampage, in which a hijacked truck was driven into a crowded Christmas market.
The attack claimed 12 lives. Tunisian suspect Anis Amri was shot dead four days later in Italy after firing at police there.
Shortly after the attack Fedpol began investigations to determine if Anis Amri had stayed in Switzerland, but could not establish a link, according to news agency ATS.