Salaev's son, Elman, told an RFE/RL correspondent in a telephone interview that his father is being held at the National Security Ministry. He said the authorities have told him that Salaev will be in custody for 48 hours.
The elder Salaev was president of the Azerbaijani Academy of Science during the 1980s.
The younger Salaev is a deputy leader of the Azerbaijani Democrat Party, an opposition group.
Azerbaijan is holding parliamentary elections on 6 November. The country has recently been criticized by the European Union for violating basic political freedoms in the run-up to the elections.