The woman, identified as Afghan police Sgt. Nargas, had entered a strategic compound in the heart of the capital and shot the adviser with a pistol as he came out of a small shop with articles he had just bought, Kabul Governor Abdul Jabar Taqwa told The Associated Press.
The woman was taken into Afghan custody shortly after the attack.
Earlier, she had asked bystanders where the governor's office was located, the governor said. As many Afghans, the policewoman uses only one name.
A NATO command spokesman, U.S. Air Force Lt. Col. Lester T. Carroll, said the woman was arrested after the incident. The slain adviser was a contractor whose identity wasn't immediately released.
The attack occurred outside the police headquarters in a walled, highly secure compound which also houses the governor's office, courts and a prison. Kabul Deputy Police Chief Mohammad Daoud Amin said an investigation was under way.
He said Nargas, a mother of four, had worked with a human rights department of the police for two years and had earlier been a refugee in Pakistan and Iran. She could enter the compound armed because as a police officer she was licensed to carry a pistol, the police official said. Amin did not know whether the killer and victim were acquainted.
"We can confirm that a civilian police adviser was shot and killed this morning by a suspected member of the Afghan uniformed police. The suspected shooter is in Afghan custody," Carroll said.
Canadian Brig. Gen. John C. Madower, a command spokesman in Kabul, called the incident "a very sad occasion" and said his "prayers are with the loved ones of the deceased."
The killing came just hours after an Afghan policeman shot five of his colleagues at a checkpoint in northern Afghanistan late Monday. The attacker then stole his colleague's weapons and fled to join the Taliban, said deputy provincial governor in Jawzjan province, Faqir Mohammad Jawzjani.
More than 60 international allies, including troops and civilian advisers, have been killed by Afghan soldiers or police this year, and a number of other insider attacks as they are known are still under investigations. NATO forces, due to mostly withdraw from the country by 2014, have speeded up efforts to train and advise Afghan military and police units before the pullout.
The surge in insider attacks is throwing doubt on the capability of the Afghan security forces to take over from international troops and has further undermined public support for the 11-year war in NATO countries.
It has also stoked suspicion among some NATO units of their Afghan counterparts, although others enjoy close working relations with Afghan military and police.
As such attacks mounted this year, U.S. officials in Kabul and Washington insisted they were "isolated incidents" and withheld details. An AP investigation earlier this month showed that at least 63 coalition troops — mostly Americans — had been killed and more than 85 wounded in at least 46 insider attacks. That's an average of nearly one attack a week. In 2011, 21 insider attacks killed 35 coalition troops.
There have also been incidents of Taliban and other militants dressing in Afghan army and police uniforms to infiltrate NATO installations and attack foreigners.
In February, two U.S. soldiers — Lt. Col. John D. Loftis and Maj. Robert J. Marchanti, died from wounds received during an attack by an Afghan policeman at the Interior Ministry in Kabul. The incident forced NATO to temporarily pull out their advisers from a number of ministries and police units and revise procedures in dealing with Afghan counterparts.
The latest known insider attack took place Nov. 11 when a British soldier, Capt. Walter Reid Barrie, was killed by an Afghan army soldier during a football match between British and Afghan soldiers in the restive southern province of Helmand.
More than 50 Afghan members of the government's security forces also have died this year in attacks by their own colleagues. Taliban militants claim such attacks reflect a growing popular opposition to both foreign military presence and the Kabul government.
In Sunday's attack, Jawzjani, the provincial official, said the attacker was an Afghan policeman manning a checkpoint in Dirzab District who turned his weapon on five colleagues before fleeing to the militant Islamist group.