The activists tried to show black flags to Modi near Ambedkar circle but were pushed away by BJP supporters before the Gujarat Chief Minister passed from there, BJP sources said.
They claimed that the activists were associated with Rastravadi Jantantrik Sena.
Police said no case has been lodged in this connection.
Modi was here along with BJP president Rajnath Singh to launch the party's campaign in Rajasthan, where elections are due later this year.
