The suspect, an unnamed 40-year-old German citizen, will come before a judge later in the day, the police and the public prosecutor said in a joint statement.
The raids at four sites in the German capital - including on properties in Charlottenburg and Reinickendorf - allowed police to "seize weapons, weapon parts and large quantities of ammunition," according to the statement, which did not give details about the type of arms found.
"Due to concerns they could be used for attacks, Berlin prosecutors took over the investigation," the authorities said.
"After it was determined that (the suspect) displayed an increased willingness to use violence, it was decided to arrest him. The suspicion of weapon possession was confirmed, without any evidence so far of a concrete attack plan."
The suspect came to their attention in the course of another criminal probe, they added.
German police have been on high alert to the threat of Islamist attacks, particularly after a truck rampage claimed by the Islamic State group killed 12 people in Berlin last December.
A report published last month found that Berlin authorities had missed several opportunities to arrest and deport the driver, Tunisian asylum seeker Anis Amri.
Officials admitted a series of security failures that allowed Amri to register under multiple identities and evade authorities while he was in contact with Islamist militants.