Santhosh was attacked by a four-member gang when he was returning home from a party last night, they said.
They said he was murdered over previous enmity and added that two people were arrested in the case while a hunt was on for two others.
Meanwhile, the Karnataka unit of the BJP claimed that Santhosh was a party worker and the incident took place when he was putting up party flags and buntings in Chennappa Garden area in view of Prime Minister Narendra Modi's visit to the city on February 4.
"When will this cycle of violence stop in Karnataka Santosh was stabbed in the thigh and died during treatment," it alleged.
More From This Section
On January 3, Deepak Rao (28), who was associated with the Bajrang Dal and the Vishwa Hindu Parishad, was killed, triggering tension in Dakshina Kannada district and leading to a retaliatory attack that claimed the life of Basheer (47).
A series of killings of Hindu activists in the state triggered a political slugfest between the ruling Congress and the BJP in recent months.
The Congress had charged the BJP with polarising the sensitive situation in the region with an eye on the upcoming Assembly polls due this year.