The reserve troops will be trained by military officials and will be "ready to defend, with the people, the sovereignty and greatness of this land", Chavez said during his weekly radio and television show on Sunday.
"If anyone were to come here and to try to seize the fatherland from us, we would make him bite the dust," he said.
The reserve troops will serve under Military Reserve Commander Julio Quintero Viloria, a staunch Chavez ally.
Chavez did not say who the enemy could be, but he has repeatedly accused the US of planning to invade Venezuela and seize its bountiful oil reserves.
He has also said the US was behind the failed two-day coup in 2002, which Washington was slow to condemn.
Chavez is a strong critic of the US
and an admirer of Fidel Castro
US officials have denied the claims and have criticised Venezuela's purchase of 100,000 Kalashnikov rifles from Russia, which they say could end in the hands of armed rebels in the continent.
Venezuelan officials say that the arms will only be used by the military.
The US is Venezuela's top oil buyer, but relations have been tense due to Chavez's strong criticism of US policy in Iraq.
However, the president said this week that he did not want to be "an enemy" of Washington, and a US senator met Chavez on Saturday in an attempt to improve relations.