A farmer in southern Egypt was arrested after putting the military chief's name and an army-style cap on his donkey.
Eight people were detained elsewhere in the country for spraying anti-military graffiti.
The arrests point to a long-standing taboo in Egypt against criticising the country's powerful military, an offence magnified amid the crackdown on supporters of ousted president Mohammed Mursi and his Muslim Brotherhood.
The farmer, Omar Abul-Magd, was arrested late on Friday in Qena province for allegedly insulting General Abdel-Fattah el-Sisi when he rode the donkey through town, the state Middle East News Agency reported.
Sisi led the military's ousting of Mursi in July and has been hailed by millions of Egyptians as an icon. His detractors, however, have called him a traitor and a murderer for overseeing the coup and the subsequent attacks on Mursi's mostly Islamist supporters, including an August raid on two pro-Mursi sit-ins in Cairo that set off violence that killed hundreds nationwide.
At least one of the eight people arrested on Saturday for spraying graffiti against Sisi was detained in Cairo, said security officials.
Last week, a military court ordered five pro-Mursi protesters to serve from two to three years in prison for chanting against the army. The court said the defendants spread hate speech and false rumours against the military through loudspeakers.
Rights advocates fear Egypt's interim military-backed authorities are using a state of emergency that grants police broad powers of arrest to silence critics.
After the popular uprising that ousted autocratic president Hosni Mubarak in 2011, criticism of the military grew as Egypt's powerful generals took over. Activists began lashing out at the ruling generals for trying civilians in military courts and using violence against protesters.
In one case, former lawmaker and rights advocate Ziad el-Oleimi came under fire for referring to then-military ruler Field Marshal Hussein Tantawi as a donkey during a rally.