What were the circumstances? They have to have probable cause. Can't get a judge to sign a warrant without it.
Law enforcement may confiscate your phone and computer (or related equipment) for evidence collection if there’s suspicion it contains information related to criminal activities, such as fraud, harassment, or possession of illegal content, as part of their investigative efforts to compile relevant data.
In more complex scenarios, your computer could fall under civil asset forfeiture laws, where it can be seized if there is a belief that the device was used in committing a crime or was acquired with the proceeds of criminal activities. In these cases, direct evidence linking you to the crime might not be necessary for such actions to be initiated.
They dont have to charge you just to get a warrant. But the chances are they already plan to charge you. Or they wouldn't bother with the warrant.