The group Human Rights Activists says the body of 45-year-old Zahra Bahrami was buried in the north-central city of Semnan on Sunday.
The group's report, released Monday, claims Bahrami's daughter was told that the burial was done secretly to avoid the presence of Dutch diplomats or others.
The Dutch government froze official contacts with Iran last week to protest the execution.
Bahrami was convicted of possessing and selling drugs. She had been jailed since December 2009 after protests against President Mahmoud Ahmadinejad's disputed re-election.