Saya mengusap dahi saya karena sedikit demam.

Mengusap comes from the root usap, which means to wipe, to rub, or to stroke with the hand.

In this sentence, mengusap dahi saya most naturally means to rub/wipe my forehead.

A few nuances:

• wipe suggests a gentle moving motion across the skin
• rub suggests a repeated motion
• stroke sounds softer and more gentle

So the exact English choice depends on context, but rubbed my forehead is a very natural translation.

The first saya is the subject: I.

The second saya shows possession: my forehead.

So the structure is:

• Saya = I
• dahi saya = my forehead

This is normal in Indonesian. English says my forehead, but Indonesian usually says forehead my.

In Indonesian, possessors usually come after the noun.

So the pattern is:

• rumah saya = my house
• buku saya = my book
• dahi saya = my forehead

This is one of the first word-order differences English speakers notice, because English puts the possessive before the noun, while Indonesian usually puts it after.

Yes, often it can be, especially with body parts when the owner is already obvious.

So you may also hear:

Saya mengusap dahi karena sedikit demam.

That still clearly means I rubbed my forehead because I had a slight fever.

Including saya after dahi is still correct. It just makes the possession more explicit.

Dahi means forehead.

It is more specific than:

• kepala = head
• wajah / muka = face

So mengusap dahi specifically refers to touching or rubbing the forehead, not the whole face or head.

Karena means because.

It introduces the reason for the action:

• Saya mengusap dahi saya = I rubbed my forehead
• karena sedikit demam = because I was a little feverish / because I had a slight fever

You can also put the reason first:

Karena sedikit demam, saya mengusap dahi saya.

That is also correct.

Indonesian often does not use a verb like to be in the same way English does.

So:

• Saya demam can mean I have a fever or I am feverish
• sedikit demam means slightly feverish / having a slight fever

English needs something like was, am, or had, but Indonesian often leaves that unstated.

That is why karena sedikit demam works without an extra verb.

It is understandable, but many speakers would probably say agak demam more naturally in everyday speech.

Compare:

• sedikit demam = a little feverish
• agak demam = somewhat feverish
• demam ringan = a mild fever

So your sentence is grammatical and understandable, but agak demam may sound more idiomatic in casual conversation.

For example: Saya mengusap dahi saya karena agak demam.

The base word is usap.

The prefix meng- is part of the Indonesian meN- verb system, which commonly forms active verbs.

So:

• usap = wipe/rub
• mengusap = to wipe/rub

This is a very common pattern in Indonesian:

• ambil → mengambil
• usap → mengusap

Here, mengusap is an active transitive verb, meaning it takes an object:

• mengusap dahi saya = rub my forehead

Saya is more neutral and polite.
Aku is more casual and personal.

So:

• Saya is safe in most situations
• Aku is common with friends, family, or in a more intimate tone

A more casual version of the sentence could be:

Aku mengusap dahiku karena agak demam.

Notice that my forehead can become dahiku, where -ku means my.

So both are possible, but saya sounds more standard and polite.