About a dozen members of Mr Anwar's People's Justice Party held placards calling for a boycott of Japanese products to protest Japanese authorities' refusal to allow Mr Anwar to enter the country after he arrived there from Malaysia on Sunday.
"Why is Japan following this kind of trend as a democratic and developed country?" the party's youth wing chief Shamsul Iskandar told reporters after handing over a protest letter to embassy officials.
"There must be a sense of respect. He (Anwar) is the opposition leader," Mr Shamsul said, adding that even if the ban was merely a result of technicality, "we want a published apology from the Japanese government."
Mr Anwar, in a statement issued Sunday, said he was "forcibly evicted from Japan" after arriving at Narita Airport earlier that day from Kuala Lumpur, being told by immigration authorities "to board the first flight back home or face deportation."
"When I asked why I was not allowed to enter, they told me that it was because of my previous conviction in 1999," he said. In 1999, Mr Anwar was sacked as deputy prime minister and jailed on corruption charges, which he says were trumped up to thwart his political rise.
"I told them this could not be a valid reason on account of the fact that prior to this I had already entered Tokyo without hindrance on three previous occasions in 2006, 2009 and 2012," he said.
Mr Anwar suggested the Malaysian government was behind what happened at Narita and demanded an explanation from Malaysian Foreign Minister Anifah Aman.
Mr Anifah later denied having any role in the affair, telling reporters late Monday that he understands Japanese authorities barred Mr Anwar from entering as they found him "undesirable."
But a Japanese Embassy official blamed "misunderstanding of procedure" on Mr Anwar's part.
The official said even though Malaysians visiting Japan for short-term stays no longer requires visas, after a visa exemption arrangement came into effect last July, Mr Anwar must still apply for a special visa before each visit due to his past conviction.
Japan's immigration law prohibits entry of people with a prior conviction who had been sentenced to imprisonment of one year or more unless they are granted special permission.
The embassy official said it could not consider a "special arrangement" for Mr Anwar this time because it received no prior application, while Mr Anwar waived his right to appeal for special treatment while still at the airport after being denied entry.
In his statement, Mr Anwar said that prior to his departure for Tokyo, his office had inquired with the Japanese Embassy "and was informed that there would be no issues outstanding that would be an impediment to my entering the country."
"I protest in the strongest terms this unwarranted action of the Japanese government in refusing me entry and denying my legitimate rights to travel freely without let or hindrance. It is indeed inconceivable for one of the world's leading democracies to take this unprecedented action under such tenuous grounds and leaves me with the impression that hidden hands may be at work here," he said.
Mr Anwar said he had gone to Tokyo on a personal invitation from Nippon Foundation chairman Yohei Sasakawa to present a paper on Muslim democrats.