A suicide bomber killed 19 people and wounded 75 others when she blew herself up in a crowd of people who had stopped in Iskandiriyah for their evening meal on Thursday.
While on Friday, one person was killed and nine wounded in an attack in eastern Baghdad.
More than 40,000 soldiers and police have been mobilised, including 2,000 female security workers, to boost security in and around Karbala for the Shia festival which begins on Sunday.
Hundreds of snipers have been deployed on rooftops and Iraqi security forces said they will search pilgrims and use bomb-sniffing dogs to detect explosives.
|More than 40,000 police and soldiers have been deployed in Karbala [EPA]
"We have set up scores of watch towers, and have cameras placed in open areas, crossroads and major entrances," Major-General Raad Shakir, Kerbala police chief, said.
Last year's pilgrimage was marred by gunbattles between Shia factions and the Iraqi security forces.
"Thank God the situation is under control. We haven't observed any security violations. People are happy and co-operating with security forces," Captain Abdullah Muhammad of the Iraqi army in Kerbala said.
"This year we haven't seen the pilgrims holding pictures of clerics or shouting against the government like last year."
Tens of thousands of people are making their way to Karbala to commemorate the birth of Imam al-Mehdi, who Shia believe will vanished centuries ago but will return to bring peace.
"We come every year. Last year my son was wounded by a bullet during the pilgrimage, but I insisted on coming again anyway. This year the situation is more secure and organised," Najim Muhammad al-Lami, who had walked for six days with his wife and two children from the southern city of Basra, said.