The move comes as Iran faces the threat of US military action in response to the killing of peaceful demonstrators and over possible mass executions.
The EU listed the Guard as a terror group last week over its part in the bloody crackdown on nationwide protests in January that killed thousands and saw tens of thousands detained.
Other countries, including the US and Canada, have previously designated the Guard as a terrorist organisation. While the move is largely symbolic, it does add to the economic pressure squeezing Iran, particularly has the Guard has a major influence on the country's economy.
Iranian Foreign Ministry spokesman Esmail Baghaei told journalists the ambassadors had begun to be summoned on Sunday and that process went into Monday as well.
"A series of actions were reviewed, various options are being prepared and were sent to the related decision-making bodies," Baghaei said.
"We think that in coming days, a decision will be made about a reciprocal action by the Islamic Republic of Iran toward the illegal, unreasonable and very wrong move by the EU."
Also Sunday, Iran's parliament speaker said the Islamic Republic now considers all European Union militaries to be terrorist groups, citing a 2019 law.
The Guard emerged from Iran's 1979 Islamic Revolution as a force meant to protect the Shiite cleric-overseen government and was later enshrined in its constitution. Operating in parallel with the country's regular armed forces, it grew in prominence and power during a long and ruinous war with Iraq in the 1980s. Though it faced possible disbandment after the war, Supreme Leader Ayatollah Ali Khamenei granted it powers to expand into private enterprise, allowing it to thrive.
The Guard's Basij force likely was key in putting down the demonstrations, starting in earnest from January 8, when authorities cut off the internet and international telephone calls for the nation of 85 million people.
Videos that have come out of Iran via Starlink satellite dishes and other means show men likely belonging to its forces shooting and beating protesters.