"Dozens of young Moroccans attempted to cross" into Melilla from the border town of Nador on New Year's Eve, the Moroccan Association for Human Rights (AMDH) said on Twitter.
Several successfully entered the Spanish territory "despite police deployment there", said a local chapter of the migrant rights group.
There was no immediate confirmation from either the Moroccan or Spanish authorities.
Melilla and its sister enclave of Ceuta have long been a magnet for Africans seeking to escape poverty and violence.
A mass attempted crossing into Melilla in late June left at least 23 people dead, according to Moroccan authorities.
Around 2,000 people, many of them Sudanese, stormed the frontier in an attempt to reach Spanish territory, leading to the worst death toll in years of attempted crossings.
Some rights groups gave a higher figure than the official toll. AMDH has said at least 27 died.
Morocco has handed dozens of migrants sentences of up to three years' imprisonment on charges including illegal entry and violence against law enforcement officers over the June 24 tragedy.
Both governments have insisted the migrants were to blame but Amnesty International conducted analysis and interviews which, it said in December, showed that Spanish and Moroccan authorities used excessive force during the incident.
Spain's public prosecutor later closed an investigation, saying no evidence of criminal wrongdoing by Spanish security forces had been found.