The 38-year-old claimed healthcare workers and the media were behind what he called “the Covid farce” and urged his followers to attack officials and institutions, police said in a statement.
They added that the man wrote in one of his messages that “all of this would be solved with a shot in the back of Pedro Sanchez's head”.
In other posts he called for Spain's college of physicians to be burned down, threatened to himself set fire to a newspaper office in the northeastern region of Aragon and asked his followers to help him find the addresses of several journalists who he said he wanted to “give a good scare” to.
The man, who was not identified, also allegedly passed himself off as a government official in calls he made to old age homes, hospitals, media outlets and football clubs to spread “false information” about the pandemic.
Police said they arrested the man in the town of Cuarte de Huerva just south of Zaragoza, the capital of Aragon. He faces charges of inciting hatred, inciting violence, making threats, slander and usurpation of public functions.
His arrest comes as Spain, one of the countries hardest hit by the pandemic, is grappling with a new surge in Covid-19 infections.
The number of confirmed cases of the respiratory disease surpassed 400,000 this week. Nearly 29,000 people have died.