The arrests came as European nations scramble to halt a surge in young people wanting to travelling to Iraq and Syria to fight with the jihadists.
Two of the suspects were arrested in Melilla, the Spanish enclave neighbouring Morocco, in the latest operation by Spain's authorities targeting such recruiting networks.
The others were detained in Girona and Barcelona in Spain's northeast.
The two arrested in Melilla were said to be behind the creation and operation of several Internet platforms spreading propaganda, particularly for the Islamic State group, the interior ministry said in a statement.
"In line with the strategy of the Daesh terrorist group, they focused on the recruitment of women who, after a process of indoctrination, would end up joining the terrorist group in conflict zones," it said, referring to the Arabic name for IS.
Private home visits were also organised for recruiting purposes and a number of young people had begun preparations to travel to war zones, the ministry said.
One of those arrested ran a "virtual community" with Islamic State propaganda and more than 1,000 subscribers, it said.
On Facebook, he had a "multitude of subscribers" outside Spain, including Latin America and countries such as Belgium, France, Morocco, Pakistan, Saudi Arabia, Tunisia, Turkey and the United States, the statement said.
One of the suspects arrested in Spain's northeast was described as an Islamic State sympathizer-turned-propagandist. The other was said to have published video to recruit potential jihadists.
Authorities were working to establish links between the two in Melilla and those in Spain's northeast.
Spain has dismantled several similar networks, particularly in Melilla and its other African enclave, Ceuta. The two enclaves constitute the only land borders between Africa and Europe.
Authorities estimate that around 100 Spanish nationals have joined jihadist fighters in Iraq and Syria, a lower number than those from France, Britain and Germany.
Britain says some 500 people have travelled from the country to join jihadist groups, while France says about 1,400 residents have either joined the jihadist cause in Syria and Iraq or were planning to do so.
France on Monday announced that it had confiscated the passports of six suspected would-be jihadists and would ban another 40 from travelling.